Ahpra registration PHY0002298174
How these guides are written and reviewed →
Giant cell myocarditis is a rare condition in which the immune system attacks the muscle of the heart. It is named after the appearance of the cells seen when a sample of heart muscle is examined under a microscope. It matters because it moves quickly: over weeks rather than years it can cause heart failure, dangerous disturbances of heart rhythm, and interruption of the heart’s electrical conduction. It is treated with medicines that suppress the immune system, and a proportion of people need mechanical support for the heart or a transplant. Physiotherapy has no role at all in the acute phase — exercise is unsafe while the heart muscle is actively inflamed, and this is one of the few conditions in this library where that is stated without qualification. Its role comes afterwards, in recovery from critical illness, from mechanical support or from transplant. This page explains the condition and where rehabilitation fits, and where it does not.
Definition
Myocarditis means inflammation of the myocardium, the muscular wall of the heart that does the pumping. Most myocarditis follows a viral infection, is mild, and settles on its own. Giant cell myocarditis is different. It is thought to be autoimmune rather than infectious, it is far more aggressive, and it does not resolve without treatment.
The name comes from the microscope. A sample of heart muscle shows widespread destruction of muscle cells alongside large multinucleated cells — giant cells — among the inflammatory cells. That appearance is what distinguishes it from other forms of myocarditis, and it is why diagnosis usually depends on obtaining a tissue sample rather than on scans or blood tests alone.
It is rare. Most cardiologists will see very few cases, and it is often not the first diagnosis considered, because it presents looking like more common problems.
Pathophysiology
Immune cells infiltrate the heart muscle and destroy working muscle cells, replacing them with inflammation and eventually with scar. Three consequences follow, and a person may present with any one of them.
The pump weakens
Losing working muscle reduces the force of each contraction, so the heart cannot move blood forward as effectively. This produces the picture of heart failure — breathlessness, particularly lying flat, swelling of the legs and abdomen, fatigue and reduced capacity for effort. In giant cell myocarditis this can develop over a few weeks, which is unusually fast.
The rhythm becomes unstable
Inflamed and scarring muscle conducts electricity unevenly, which creates the conditions for ventricular arrhythmias — fast, disorganised rhythms arising from the main pumping chambers. These are dangerous, they can occur without warning, and they are a common way for the condition to first present.
Conduction is interrupted
The heart’s electrical wiring runs through the muscle that is being destroyed. Damage to it causes heart block, in which signals from the upper chambers fail to reach the lower ones. This can cause blackouts and may require a pacemaker urgently.
This combination — a failing pump, an unstable rhythm and unreliable conduction, all developing quickly — is what makes the condition serious and what shapes every decision about activity.
Symptoms
There is no single presentation, and that is part of the diagnostic difficulty. Common ones include:
- New heart failure in someone previously well, developing over weeks, often initially attributed to a chest infection or to asthma.
- Palpitations, collapse or cardiac arrest from ventricular arrhythmia, sometimes as the very first symptom.
- Blackouts or extreme slowing of the pulse from heart block.
- Chest pain with raised cardiac blood markers, which looks initially like a heart attack and is investigated as one.
Some people have another autoimmune condition already, and giant cell myocarditis is recognised to occur alongside conditions such as inflammatory bowel disease, thyroid disease and thymoma. Most people, however, have no relevant history at all.
Unlike most conditions in this library, the acute phase of giant cell myocarditis is managed in hospital and often in intensive care. If you have been diagnosed, or are being investigated for possible myocarditis, seek emergency help for:
- Blackout, near-blackout, or collapse.
- Palpitations that are fast, sustained, or accompanied by light-headedness or chest pain.
- Breathlessness that is worsening over hours or days, or that wakes you at night or prevents you lying flat.
- Chest pain.
Do not exercise while myocarditis is active or being investigated, and do not resume training on the basis of feeling better. Exertion during active inflammation of the heart muscle raises the risk of dangerous arrhythmia. Clearance to exercise is a cardiology decision based on tests, not on symptoms.
Diagnosis
Investigation moves quickly and usually happens in hospital:
- ECG — looking for arrhythmia, heart block and changes suggesting myocardial injury.
- Blood tests — cardiac troponin, markers of inflammation, and tests for other causes.
- Echocardiography — assessing how well the chambers are contracting and excluding valve disease.
- Cardiac MRI — showing inflammation, oedema and scarring in the muscle, and where in the wall they sit.
- Endomyocardial biopsy — a small sample of heart muscle taken via a catheter. This is what makes the specific diagnosis, and giant cell myocarditis is one of the clearest indications for performing it, because the treatment differs so much from other forms.
- Coronary assessment — to exclude a heart attack, which presents similarly.
Management
Suppressing the immune attack
The central treatment is immunosuppression, usually combining glucocorticoids with other agents such as ciclosporin, and sometimes additional drugs. Started early, this changes the course of the illness substantially compared with the outcomes reported before immunosuppression was used. Treatment often continues long term, and stopping it carries a real risk of the condition returning.
Supporting the heart
Standard heart failure treatment is used alongside — medicines to reduce the work of the heart and manage fluid. Where the pump is severely affected, temporary mechanical support may be needed, and some people go on to a ventricular assist device or heart transplant. Giant cell myocarditis is one of the recognised reasons for transplantation in younger adults.
Protecting against arrhythmia
Because dangerous rhythms are a major risk, an implantable defibrillator is frequently considered, and a pacemaker may be needed if conduction is affected. Decisions about timing depend on whether the inflammation is expected to settle with treatment.
Recovery and what comes after
Outcomes have improved considerably with early diagnosis and immunosuppression, and some people recover substantial heart function. Others are left with lasting impairment of the pump, or reach recovery by way of a transplant. In all of these situations the person emerging from the acute illness is usually profoundly deconditioned:
- Muscle loss from weeks of bed rest, critical illness and high-dose steroids — often severe, and not something that recovers on its own.
- Very low exercise tolerance, sometimes to the point where ordinary daily activity is exhausting.
- Understandable fear of exertion, particularly in anyone who collapsed or was resuscitated. This is a rational response to what happened, and it needs addressing directly rather than being dismissed.
- A device in place, which changes some activities but rules out far less than most people assume.
- Long-term immunosuppression, with its implications for infection risk and bone health.
This is the point at which supervised rehabilitation becomes not just safe but valuable — and it should be supervised, with monitoring, precisely because of the history.
Exercise after giant cell myocarditis
Two things need saying plainly, because they pull in opposite directions and both are true.
The first is that exercise during active myocarditis is unsafe, and the restriction is not a formality. Return to exercise follows assessment — typically imaging, rhythm monitoring and often an exercise test — and is authorised by the cardiology team. No physiotherapist should be progressing exercise in this condition without that clearance, and we will not.
The second is that once clearance is given, avoiding activity causes its own harm. Deconditioning after critical illness is severe, it does not resolve spontaneously, and it accounts for a great deal of the breathlessness and fatigue people attribute to their heart. Supervised, monitored, progressive exercise is the treatment for it, and in cardiac populations generally it improves capacity, symptoms and confidence.
The practical answer is a programme built around your cardiology team’s parameters, with monitoring during sessions, starting conservatively and progressing on measurement rather than on how a session felt.
How it differs from other kinds of myocarditis
Most people who develop myocarditis have a form that behaves quite differently, and knowing which one you have determines the treatment. This is worth understanding because it explains why a biopsy was taken.
Viral (lymphocytic) myocarditis
This is the common form, typically following a viral illness. Under the microscope the inflammatory cells are lymphocytes, without giant cells. Most cases settle over weeks to months with rest and standard heart failure medicine, and immunosuppression is not routinely used. The exercise restriction during the acute phase applies here too, but the outlook is generally better and the treatment less intensive.
Cardiac sarcoidosis
This is the condition giant cell myocarditis is most often confused with, and the distinction can be genuinely difficult. Both cause heart failure, ventricular arrhythmia and heart block, and both can show giant cells on a biopsy. The difference is that sarcoidosis forms organised granulomas and usually affects other organs — most often the lungs and lymph nodes — while giant cell myocarditis does not form granulomas and is generally confined to the heart. Distinguishing them matters because the intensity and duration of immunosuppression differ, as does the expected course.
Immune checkpoint inhibitor myocarditis
Some modern cancer treatments can cause a severe myocarditis that resembles giant cell myocarditis closely, including on biopsy. If you are receiving or have recently received immunotherapy for cancer, this is an important part of the picture and your oncology team will be involved in decisions.
In practice these distinctions are made by the cardiology team using the biopsy, imaging and the pattern of involvement elsewhere in the body. From a rehabilitation standpoint the relevance is straightforward: the diagnosis determines how long inflammation is expected to persist, and therefore how cautiously exercise is reintroduced and how closely it is monitored.
Questions worth asking your cardiology team
Rehabilitation after this condition depends on information that only your treating team holds. These are the questions that most change what a physiotherapist can safely do, and it is reasonable to ask for the answers in writing:
- Am I cleared for exercise, and at what intensity? A specific answer — a heart rate ceiling, a rating of perceived exertion limit, or a wattage — is far more useful than general encouragement.
- What is my current ejection fraction, and when was it last measured? This shapes both the programme and the monitoring.
- Has my rhythm been assessed recently, and was any arrhythmia found?
- If I have a defibrillator, what is the therapy threshold? Knowing the rate at which the device will act sets a hard ceiling for training.
- Are there activities I should avoid entirely? Heavy lifting and sustained straining are common restrictions, particularly after device implantation or transplant.
- What symptoms should stop me, and who do I contact?
Bring the answers, along with your discharge summary and recent clinic letters, to a first physiotherapy appointment. A programme built on documented parameters is both safer and more useful than one built on assumptions.
Warning signs
Role of the physiotherapist
Physiotherapy plays no part in treating the inflammation itself, and no part at all in the acute illness. Where it matters is recovery: rebuilding what critical illness, prolonged bed rest, steroids and in some cases transplant surgery have taken.
We will not begin exercise rehabilitation in this condition without documented clearance from your cardiologist, including any limits on heart rate, intensity or activity type. That is a firm position, not a cautious one, and it is the reason to bring your discharge summary and clinic letters to a first appointment.
- Physiotherapy Assessment — establish a baseline of strength, exercise tolerance and breathing pattern within the limits your cardiology team has set
- Cardiorespiratory Rehabilitation — supervised, monitored exercise with oxygen saturation and heart rate watched throughout — the treatment for deconditioning after critical illness
- Post-Surgical Rehabilitation — structured recovery after device implantation, assist device or transplant, working inside the surgical team’s protocol
- Functional Capacity Assessments — objective documentation of function where a plan, an employer or an insurer requires it
Clinical evidence
Part 1 covers the same condition without the technical detail. What follows is the evidence base behind it, written for clinicians — the literature, the reasoning and the gaps.
For clinicians: this summary supports clinical reasoning and is not a protocol. Check current guidelines and local policy before applying it, and read it alongside the key references and guidelines directory.
Framing. Giant cell myocarditis is a rare, idiopathic, predominantly T-lymphocyte-mediated myocarditis characterised histologically by multinucleated giant cells, extensive myocyte necrosis and absence of granuloma formation — the last being the principal histological discriminator from cardiac sarcoidosis, with which it shares much of its clinical presentation.1,2 The multicentre registry reported by Cooper and colleagues remains the defining natural-history dataset, describing a median transplant-free survival of approximately 5.5 months in the pre-immunosuppression era.1 Contemporary series report substantially better outcomes with early immunosuppression, though selection and ascertainment bias are difficult to exclude in a disease of this rarity.3,4
Presentation and diagnosis
- Presentation is heterogeneous: rapidly progressive heart failure, ventricular arrhythmia, high-grade atrioventricular block, or an acute coronary syndrome mimic.
- Endomyocardial biopsy is central, and giant cell myocarditis is among the strongest indications for it in the ESC position statement on myocardial and pericardial disease, because the histological diagnosis directly determines immunosuppressive management.2,5
- Sampling error is a recognised limitation given patchy involvement, and repeat or image-guided biopsy is sometimes required.
- Cardiac magnetic resonance contributes to localisation and to assessment of oedema and fibrosis, but does not substitute for histology in this diagnosis.6
- Coexisting autoimmune disease is reported in a minority, notably inflammatory bowel disease and thymoma.1
Management
- Combination immunosuppression is standard — most commonly corticosteroid with ciclosporin, with additional agents in some protocols — and registry data associate earlier initiation with improved transplant-free survival.3,4
- Guideline-directed heart failure therapy is used concurrently.
- Mechanical circulatory support and cardiac transplantation are established in refractory disease, and recurrence in the allograft is documented — relevant when counselling post-transplant patients about long-term surveillance.1,7
- Device therapy decisions are individualised, complicated by the possibility of inflammatory-phase arrhythmia resolving with immunosuppression.
Exercise restriction in the acute phase — the strongest recommendation on this page. Current ESC guidelines on sports cardiology and exercise in patients with cardiovascular disease recommend abstention from moderate and high-intensity exercise during acute myocarditis, with return to sport considered only after a defined interval and following reassessment including imaging and rhythm monitoring.8 The mechanistic rationale is that exertion during active myocardial inflammation is arrhythmogenic; the epidemiological rationale is myocarditis’s consistent representation among causes of sudden cardiac death in young athletes.9 In giant cell myocarditis specifically, where arrhythmic burden is high and the inflammatory process is aggressive and persistent, extrapolating a fixed return interval from lymphocytic myocarditis is not defensible. Clearance must be individualised by the treating cardiology service and documented. A physiotherapy service should decline to progress exercise in this diagnosis in the absence of that documentation — this is a scope and safety boundary, not a matter of clinical preference.
Rehabilitation after the acute phase
- There is no disease-specific trial evidence for exercise rehabilitation in giant cell myocarditis, and given its incidence there is unlikely to be.
- Cardiac rehabilitation in heart failure — HF-ACTION and subsequent meta-analyses support improved exercise capacity and quality of life with an acceptable safety profile.10,11
- Rehabilitation after cardiac transplantation — supervised training improves peak oxygen uptake despite chronotropic abnormality.12
- Rehabilitation after critical illness, addressing ICU-acquired weakness.13
- The mechanistic overlap justifies extrapolation, and it should be described to patients as extrapolation.
Practical parameters where clearance exists
- Symptom-limited exercise testing prior to prescription, where the cardiology team supports it.
- Continuous heart rate and rhythm awareness during early sessions, with saturation monitoring.
- Conservative initial intensity, with progression governed by measured response rather than session tolerance.
- Explicit ceilings where an assist device or defibrillator is in situ, taken from the implanting service.
- Progressive resistance training to address steroid-associated and disuse myopathy, which is frequently the dominant impairment and is under-treated relative to aerobic work.
Psychological sequelae
- Exertional fear-avoidance, anxiety and post-traumatic symptoms are common in survivors of arrhythmic presentation, resuscitation, mechanical support or transplantation.
- This is a well-described determinant of rehabilitation uptake and outcome in cardiac populations.
- Monitored exercise has a role beyond its physiological effect: supervision with visible monitoring is what allows a patient who arrested during exertion to attempt exertion again.
- Where symptoms are prominent, psychological referral should be concurrent rather than sequential.
Evidence gaps
- Optimal timing of rehabilitation initiation after immunosuppression is uncharacterised.
- Whether rehabilitation gains persist through relapse is unknown.
- The interaction between long-term immunosuppression, steroid myopathy and training response has not been studied in this population.
- These should be presented as reasoned judgement rather than evidence.
References for the clinical evidence summary
- Cooper LT Jr, Berry GJ, Shabetai R; Multicenter Giant Cell Myocarditis Study Group. Idiopathic giant-cell myocarditis — natural history and treatment. N Engl J Med 1997;336(26):1860–1866.
- Caforio ALP, Pankuweit S, Arbustini E, et al. Current state of knowledge on aetiology, diagnosis, management and therapy of myocarditis: a position statement of the ESC Working Group on Myocardial and Pericardial Diseases. Eur Heart J 2013;34(33):2636–2648.
- Kandolin R, Lehtonen J, Salmenkivi K, Räisänen-Sokolowski A, Lommi J, Kupari M. Diagnosis, treatment, and outcome of giant-cell myocarditis in the era of combined immunosuppression. Circ Heart Fail 2013;6(1):15–22.
- Ammirati E, Veronese G, Brambatti M, et al. Fulminant versus acute nonfulminant myocarditis in patients with left ventricular systolic dysfunction. J Am Coll Cardiol 2019;74(3):299–311.
- Cooper LT, Baughman KL, Feldman AM, et al. The role of endomyocardial biopsy in the management of cardiovascular disease: a scientific statement from the AHA, ACC and ESC. Circulation 2007;116(19):2216–2233.
- Ferreira VM, Schulz-Menger J, Holmvang G, et al. Cardiovascular magnetic resonance in nonischemic myocardial inflammation: expert recommendations. J Am Coll Cardiol 2018;72(24):3158–3176.
- Elamm CA, Al-Kindi SG, Bianco CM, Dhakal BP, Oliveira GH. Heart transplantation in giant cell myocarditis: analysis of the United Network for Organ Sharing registry. J Card Fail 2017;23(7):566–569.
- Pelliccia A, Sharma S, Gati S, et al. 2020 ESC Guidelines on sports cardiology and exercise in patients with cardiovascular disease. Eur Heart J 2021;42(1):17–96.
- Maron BJ, Doerer JJ, Haas TS, Tierney DM, Mueller FO. Sudden deaths in young competitive athletes: analysis of 1866 deaths in the United States, 1980–2006. Circulation 2009;119(8):1085–1092.
- O’Connor CM, Whellan DJ, Lee KL, et al. Efficacy and safety of exercise training in patients with chronic heart failure: HF-ACTION randomized controlled trial. JAMA 2009;301(14):1439–1450.
- Long L, Mordi IR, Bridges C, et al. Exercise-based cardiac rehabilitation for adults with heart failure. Cochrane Database Syst Rev 2019;1:CD003331.
- Anderson L, Nguyen TT, Dall CH, Burgess L, Bridges C, Taylor RS. Exercise-based cardiac rehabilitation in heart transplant recipients. Cochrane Database Syst Rev 2017;4:CD012264.
- Connolly B, Salisbury L, O’Neill B, et al. Exercise rehabilitation following intensive care unit discharge for recovery from critical illness. Cochrane Database Syst Rev 2015;6:CD008632.
Physiotherapy plays no part in treating the inflammation, and none at all in the acute illness. Where it matters is recovery — rebuilding what critical illness, bed rest and steroids take out of you. We will not begin exercise rehabilitation without documented clearance and limits from your cardiologist.
Corrections: If something on this page is wrong, out of date or unclear, we want to know. Email reception@inspireclinic.au with the page name and what you believe is incorrect. Substantive corrections are made promptly, and the guide’s version and last-updated date are changed to reflect it.