Prognosis
The prognosis associated with myocarditis is stratified by the severity and time course along which symptoms develop. In addition to symptom severity, there are also several indicators of heart function that can be used to predict patient outcomes, many of which are part of the standard evaluation of patients presenting with cardiovascular dysfunction. An electrocardiogram is one of the most common screening tools used in cases of suspected cardiac pathology, such as myocarditis. The findings that correlate with poorer outcomes are non-specific and include widened QRS complexes and QT intervals, partial or complete atrial-ventricular heart block, and malignant ventricular arrhythmias like sustained ventricular tachycardia or ventricular fibrillation. Electrocardiogram findings of ST elevations with upward concavity and an early repolarization pattern, however, were associated with a better cardiovascular prognosis in general.In cases of acute myocarditis, cardiac magnetic resonance imaging can reveal several prognostic indicators that, similar to ECGs, are non-specific and reflect poorer cardiac physiology. Late gadolinium enhancement on cardiac MRI demonstrates perturbations in extracellular volume as a result of cell necrosis or edema, and is significantly associated with increases in all-cause mortality, cardiovascular mortality, and major adverse cardiovascular events. The association was strongest with any late gadolinium enhancement, but remained true for findings of anterolateral-specific enhancement.
Bacteria can also result in myocarditis, although it is rare in patients with normal heart function and without a preexisting immunodeficiency. A list of the most relevant infectious organisms is below. Viral: adenovirus, parvovirus B19, coxsackie virus, rubella virus, polio virus, Epstein-Barr virus, hepatitis C virus, and severe acute respiratory syndrome coronavirus 2 (SARS‑CoV‑2, causing COVID-19)
Protozoan: Trypanosoma cruzi and Toxoplasma gondii (causing Chagas disease and toxoplasmosis, respectively)
Bacterial: Brucella, Corynebacterium diphtheriae, Neisseria gonorrhoeae, Haemophilus influenzae, Actinomyces, Tropheryma whipplei, Vibrio cholerae, Borrelia burgdorferi, Leptospira, Rickettsia, Mycoplasma pneumoniae
Fungal: Aspergillus
Parasitic: Ascaris, Echinococcus granulosus, Paragonimus westermani, Schistosoma, Taenia solium, Trichinella spiralis, visceral larva migrans, Wuchereria bancrofti

Immune conditions
Allergic reaction (e.g., to acetazolamide or amitriptyline)
Kawasaki disease
Autoimmunity (scleroderma, lupus, sarcoidosis, and systemic vasculitides)
Toxic shock syndrome

Drug reactions and toxins
Anthracyclines and other forms of chemotherapy
Antipsychotics including clozapine
Alcohol
Stimulants such as mephedrone and cocaine
Arsenic
Carbon monoxide
Snake venom
Heavy metals (copper or iron)

Vaccination
Myocarditis and pericarditis can be a rare side effect of some vaccines like the smallpox vaccine. Some COVID-19 vaccination doses carry a very small risk (33 per million overall) of causing myocarditis and pericarditis, more so in young men at repeated administration. According to a meta-analysis that does not differentiate between the two mRNA-vaccines BNT162b2 and mRNA-1273, the risk is less than that associated with COVID-19 itself. In adolescent males aged 16 to 17 years the crude reporting rate of myocarditis was 105.9 per million doses of the BNT162b2 vaccine.