myocarditis

Just as a viral infection can leave your throat or muscles sore and inflamed, it can sometimes inflame the heart muscle itself. Myocarditis is inflammation of the myocardium — the heart's contractile muscle — in which immune cells flood in, the muscle swells, and contraction can weaken. It often follows a recent viral illness by days to weeks.

The presentation is highly variable. Some people have only mild chest discomfort and palpitations and recover fully; others develop chest pain that mimics a heart attack, a sudden drop in pumping power with heart failure, or dangerous rhythm disturbances. Because troponin (a blood marker of injured heart muscle) often rises and the ECG can change, distinguishing it from a true heart attack requires careful evaluation, frequently with cardiac MRI.

Common triggers include viruses, but bacteria, autoimmune diseases, and certain drugs — including some cancer immunotherapies — can also cause it. Most viral cases settle with supportive care and heart-failure treatment as needed, but a minority leave lasting muscle weakness (an inflammatory or dilated cardiomyopathy), and severe acute cases can be life-threatening, so the course is genuinely unpredictable.