Myocarditis, when the heart muscle gets inflamed, can make it harder for the heart to pump blood possibly causing chest pain, shortness of breath and irregular heartbeats. Pericarditis, when the thin lining around the heart (called the pericardium) becomes inflamed, can also cause sharp chest pain that feels worse when lying down.

The Food and Drug Administration said Wednesday it was expanded existing warnings on the two leading COVID vaccines about a rare heart side effect mainly seen in young men, despite previous guidance from the Centers for Disease Control and Prevention that said there was no increased risk.

FRIDAY, June 27, 2025 (HealthDay News) — The U.S. Food and Drug Administration (FDA) has added new warnings to the Pfizer and Moderna COVID-19 vaccines about a rare heart condition that mostly affects young men. The update expands earlier warnings about myocarditis, a type of heart inflammation, The Associated Press reported.