Does it matter if I exercise? What can ``cardiophysics" tell us?

Lower heart rates are often associated with better cardiovascular health. But there's a lot more to cardiac rhythms than just the average heart rate. Fractal analysis of inter-beat intervals shows a surprising ability to discriminate between healthy and unhealthy, young and old groups. Are the fluctuations in the heartbeat of a healthy heart random, small, periodic, or chaotic? Does exercise make a difference? We discuss our analysis of the cardiac data of two groups of individuals, those that were physically active and those that were sedentary.