The beautiful dance of the heart seems so simple when Cleveland Clinic cardiologist Dr. Mina Chung explains it. “There are four chambers in the heart,” she says. “With each normal heartbeat, the two upper chambers contract and push blood through the valves into the lower chambers. The lower chambers contract and pump blood out of the heart.” If only it was that easy. We talked to several Best Doctors about how the complex system works and what happens when it doesn’t.