I30-I52: Other forms of heart disease

I40: Acute myocarditis

Acute myocarditis is an inflammation of the heart muscle, specifically, the myocardium. It's most commonly caused by viral infections, but it can also result from bacterial, fungal or parasitic infections, allergic reactions to medications or toxins, and autoimmune diseases. People with acute myocarditis might feel like they have a heavy cold or flu, with symptoms such as fatigue, shortness of breath, rapid or irregular heartbeats, and chest pain. It can progress quickly or slowly, affecting the heart's ability to pump and causing fluid buildup in the lungs or rest of the body if left untreated. While many recover fully, severe cases can lead to life-threatening complications such as heart failure. This condition primarily affects the cardiovascular system.