I was studying for finals during my last year of school in Athens when my mom called. Dad had been complaining of fatigue and shortness of breath, so my mom, a nurse practitioner, used her stethoscope to listen to his heart. That’s when she detected a distinct murmur, one she knew he didn’t have before. It was his mitral valve. Doctors theorized that it had been damaged by rheumatic fever when he was a child, a complication that can develop if a case of strep throat isn’t treated properly. The mitral valve is one of four valves in the heart, which open to allow blood to flow through, then close to prevent it from flowing backward. That’s what makes the sound of a heartbeat.