[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [General pathology](https://durgical.com/en/general-pathology/) › [Heart](https://durgical.com/en/general-pathology/areas/heart/) › Myocarditis # Myocarditis - Lesion Myocarditis is inflammation of the heart muscle that injures myocytes. Viruses are the commonest cause, but drugs, parasites and autoimmunity also cause it. Updated Nov 12, 2026 ## Key points - Diagnosis on biopsy: inflammatory infiltrate with myocyte injury (necrosis or damage) next to the inflammatory cells. - Lymphocytic (viral) myocarditis is the commonest pattern; many patients recover, some progress to dilated cardiomyopathy. - Hypersensitivity myocarditis: eosinophil-rich perivascular and interstitial infiltrate after drugs. - Giant-cell myocarditis: multinucleated giant cells, extensive necrosis, rapidly fatal without treatment or transplant. - Lyme disease: heart block; diphtheria: toxin-mediated myocyte injury; Chagas: chronic fibrosing myocarditis. - Immune checkpoint inhibitors can cause a lymphocytic myocarditis with high mortality. ## What it is Myocarditis is inflammation of the myocardium with myocyte injury. In high-income countries most cases are viral (enteroviruses such as Coxsackie, adenovirus, parvovirus B19, SARS-CoV-2), causing direct damage and an immune response. Non-viral causes include Trypanosoma cruzi (Chagas, a major cause in Latin America), Lyme disease, diphtheria toxin, Toxoplasma, Trichinella, HIV, drug hypersensitivity, immune checkpoint inhibitors, rare mRNA vaccine reactions and autoimmune diseases. Giant-cell myocarditis is a rare, aggressive form. ## Structure - Gross: may be normal or dilated, flabby, with mottled pale and haemorrhagic areas. - Microscopy: interstitial inflammation with adjacent myocyte injury; healed lesions leave patchy fibrosis. ## Causes and patterns of myocarditis | Type | Infiltrate | Notes | | --- | --- | --- | | Viral (lymphocytic) | Lymphocytes with myocyte necrosis | Enteroviruses, adenovirus, parvovirus B19; may lead to dilated cardiomyopathy | | [Chagas disease](https://durgical.com/en/conditions/chagas-cardiomyopathy/) | Mononuclear cells, parasite nests in acute phase, fibrosis in chronic | Trypanosoma cruzi; endemic in Latin America | | [Lyme disease](https://durgical.com/en/conditions/lyme-disease/) | Lymphocytes and plasma cells near the conduction system | AV block that often resolves | | [Diphtheria](https://durgical.com/en/conditions/diphtheria/) | Little inflammation; toxin-mediated myocyte damage | Unvaccinated populations | | Hypersensitivity and drug-induced | Eosinophils, lymphocytes, macrophages | Drugs, checkpoint inhibitors | | Giant-cell myocarditis | Giant cells, lymphocytes, eosinophils, wide necrosis | Aggressive, autoimmune associations | ## Clinical notes - Presentations range from no symptoms to chest pain mimicking infarction, arrhythmias, acute heart failure or sudden death; troponin is elevated. - Cardiac MRI shows edema and patchy late enhancement; biopsy is reserved for severe or atypical cases. ## Memory aid Lymphocytes for viruses, eosinophils for drugs, giant cells for the aggressive one, and in Latin America never forget the kissing bug. ## Test yourself Think of the answer, then tap the question to see it. ## What is needed to diagnose myocarditis on biopsy? An inflammatory infiltrate associated with injury or necrosis of adjacent myocytes. ## Which viruses are classic causes of myocarditis? Enteroviruses, especially Coxsackievirus B; also adenovirus, parvovirus B19 and SARS-CoV-2. ## Which form of myocarditis carries the worst prognosis? Giant-cell myocarditis. [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/general-pathology/myocarditis/) [More Pathology questions →](https://durgical.com/en/practice/?f=pathology) ## Elsewhere in DurgiPedia - [Cancer immunotherapy: checkpoint inhibitors, CAR-T and vaccines](https://durgical.com/en/immunology/cancer-immunotherapy-checkpoint-inhibitors-car-t-and-vaccines/) - [Type IV hypersensitivity (delayed, T cells)](https://durgical.com/en/immunology/type-iv-hypersensitivity/) ## Connections ## Related 5 - [Chagas heart disease](https://durgical.com/en/general-pathology/chagas-heart-disease/) - [Dilated cardiomyopathy](https://durgical.com/en/general-pathology/dilated-cardiomyopathy/) - [Toxic and radiation injury of the myocardium](https://durgical.com/en/general-pathology/toxic-and-radiation-injury-of-the-myocardium/) - [Granulomatous inflammation: caseating vs non-caseating, the causes to know](https://durgical.com/en/general-pathology/granulomatous-inflammation-caseating-vs-non-caseating-the-causes-to-know/) - [Chronic inflammation: causes, cells and features](https://durgical.com/en/general-pathology/chronic-inflammation-causes-cells-and-features/) ## Related conditions 7 - [Myocarditis](https://durgical.com/en/conditions/myocarditis/) - [Lyme disease](https://durgical.com/en/conditions/lyme-disease/) - [Diphtheria](https://durgical.com/en/conditions/diphtheria/) - [COVID-19](https://durgical.com/en/conditions/covid-19/) - [Dilated cardiomyopathy](https://durgical.com/en/conditions/dilated-cardiomyopathy/) - [Chagas cardiomyopathy](https://durgical.com/en/conditions/chagas-cardiomyopathy/) - [Sarcoidosis](https://durgical.com/en/conditions/sarcoidosis/) ## Microorganisms 6 - [Enteroviruses](https://durgical.com/en/microbiology/enteroviruses/) - [Borrelia burgdorferi](https://durgical.com/en/microbiology/borrelia-burgdorferi/) - [Corynebacterium diphtheriae](https://durgical.com/en/microbiology/corynebacterium-diphtheriae/) - [Toxoplasma gondii](https://durgical.com/en/microbiology/toxoplasma-gondii/) - [SARS-CoV-2](https://durgical.com/en/microbiology/sars-cov-2/) - [Trypanosoma cruzi](https://durgical.com/en/microbiology/trypanosoma-cruzi/) [← All of general pathology](https://durgical.com/en/general-pathology/) Educational content on the mechanisms of disease; not a diagnostic or treatment guide and no substitute for a health professional's advice. No doses are given. Sources: [Myocarditis: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/000149.htm) (MedlinePlus, US National Library of Medicine, 2025). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/general-pathology/myocarditis/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/general-pathology/myocarditis/