The functional impairment of the heart and lungs affects oxygen and carbon dioxide transport. Alterations in cardiovascular function play a prominent role in determining the severity of impaired physiological mechanisms affecting gas exchange. The cardinal manifestations of heart failure, varying directly with the severity of the disease, are used as a guide to treatment course and prognosis. As an acute cardiac condition progresses to chronic congestive heart failure (CHF), respiratory effort is increased. Functional capacity and efficiency of gas exchange in the lungs are evaluated by objective measures of oxygen consumption. The complex nature of cardiac and lung disease is becoming increasingly relevant given the association with increased cardiac death, dysfunctional gas exchange, and overall impaired health status.