How many cases of myocarditis a year in the united states?

Hard to say: Many cases of myocarditis are clinically asymptomatic and resolve without treatment - thus hard to count. As many as 1-5% autopsies show evidence of this condition. One estimate is that there are 24,000-30,000 new cases every year.

Several thousand: Several thousand myocarditis cases are diagnosed in US each year. This is probably an underestimate. Many cases of pericarditis (inflammation of the outer lining of the heart) also extend into the myocardium. Some cases of unexplained sudden cardiac death are due to myocarditis. And because most cases of dilated cardiomyopathy are not biopsied, we probably fail to recognize many actual cases.