Firefighter and paramedic Mike Camilleri once had no trouble hauling heavy gear up ladders. Now battling long COVID, he gingerly steps onto a treadmill to learn how his heart handles a simple walk."This is, like, not a tough-guy test so don't fake it," warned Beth Hughes, a physical therapist at Washington University in St. Louis.Somehow, a mild case of COVID-19 set off a chain reaction that eventually left Camilleri with dangerous blood pressure spikes, a heartbeat that raced with slight exertion, and episodes of intense chest pain. He's far from alone. How profound a toll COVID-19 has taken on the...