Doctors explain what led to John Fetterman's stroke
John Fetterman campaigns for U.S. Senate at a meet-and-greet at Joseph A. Hardy Connellsville Airport on May 10, 2022, in Lemont Furnace, Pennsylvania. - Michael M. Santiago/Getty Images North America/TNS

The stroke that Pennsylvania Lt. Gov. John Fetterman had on Friday was caused by a clot from his heart, which was out of rhythm for too long, the U.S. Senate candidate said Sunday in a statement. That condition, called atrial fibrillation, is a common cause of strokes, but what exactly does it mean? When the heart beats normally, the left atrium, the top left chamber of the heart, beats smoothly and rhythmically, 70 times a minute, and sends blood to the chamber below, the left ventricle. "In fibrillation, the atrium's just wiggling, like a bag of worms, and it's not really squeezing," said Ma...