Myopericarditis

Myopericarditis is a combination of both myocarditis and pericarditis appearing in a single individual, namely inflammation of both the pericardium and the heart muscle. It can involve the presence of fluid in the heart. Myopericarditis refers primarily to a pericarditis with lesser myocarditis, as opposed to a perimyocarditis, though the two terms are often used interchangeably. Both will be reflected on an ECG. Myo-pericarditis usually involves inflammation of the pericardium, or the sac covering the heart.

The ACAM2000 smallpox vaccine could cause myopericarditis in some people, according to https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2880337/