Exercise stresses the primary function of the cardiovascular system, which is the supply of O<sub>2</sub> and removal of CO<sub>2</sub> from the cells of the body. Even ordinary walking requires an increase in O<sub>2</sub> consumption and CO<sub>2</sub> production by the exercising muscles of 20 times the resting level. While pulmonary dysfunction may affect arterial blood gas tensions, the dynamics of O<sub>2</sub> uptake and CO<sub>2</sub> output by the lungs depend on the circulatory responses to exercise. Thus, measurement of the dynamics of O<sub>2</sub> uptake in response to exercise has been shown to reflect cardiovascular function. Inability of the circulatory responses to meet an increased O<sub>2</sub> requirement may be reflected in abnormalities in O<sub>2</sub> uptake dynamics, and an early increase in CO<sub>2</sub> output relative to O<sub>2</sub> uptake consequent to bicarbonate buffering of lactic acid. Application of currently available technology for the continuous measurement and analysis of pulmonary gas exchange can afford the practicing or investigative cardiologist with a noninvasive and inexpensive means for assessing cardiovascular function.