Patients with pectus excavatum complain about fatigue, tachypnea, discomfort and dyspnea, but the existence of an equivalent underlying pathophysiology has been questioned. We investigated 75 teenagers (49 pectus excavatum patients and 26 age matched controls) at rest and during bicycle exercise at submaximal exercise levels. At rest cardiac function was determined using echocardiography. During rest and exercise, cardiac output, heart rate and aerobic exercise capacity were measured using photo-acoustic gas-rebreathing technique for non-invasive determination of the cardiopulmonary function. At rest, no cardiac differences were found between control subjects and patients with pectus excavatum. During submaximal exercise, cardiac index was lower 6.6(6.3-7.0) l/min/m(2) among the pectus patients as compared to the control subjects 8.0(7.3-8.8) l/min/m(2), P=0.0001. The lower cardiac output among the pectus patients was due to a lower stroke index 42(39-45) ml/beat/m(2) as compared to controls 54(44-64) ml/beat/m(2), P=0.0022, whereas heart rate was unchanged. Cardiac function is significantly impaired at submaximal exercise level compared to healthy age matched controls.