Myocarditis has many causes, including viral infection and mRNA Covid vaccination. It is often diagnosed when people go to emergency rooms with chest pain but can also occur without symptoms, causing people to have cardiac damage that is clear on heart scans or in blood tests but does not cause pain or fever. Studies have shown myocarditis requiring hospitalization may occur in as many as 1 in 3,000 teenage boys or young adult men who receive a Covid jab, with the highest risk after the second dose. Many studies show Moderna's shot, which has more mRNA than Pfizer's, has a higher risk.