Exercise places a unique stress on the body, requiring multiple organ systems to function in an efficient, coordinated manner.  As a result, monitored exercise can unmask specific limitations that aren't apparent in a resting state.  Unlike traditional exercise stress testing, which simply records electrocardiographic response to exercise, Cardiopulmonary Exercise Testing (CPET) simultaneously monitors cardiac and pulmonary function, and also provides information about the body's ability to handle exercise at the cellular level.