PURPOSE: To evaluate the effect of resting pulmonary function on metabolic responses to exercise in patients with a bicuspid aortic valve (BAV) compared to normal control subjects (C). METHODS: We evaluated 18 BAV patients and 18 C subjects, age and size matched, using a Ramp Treadmill protocol. Pulmonary function was evaluated with resting spirometry measures of Forced Vital Capacity (FVC) and Forced Expiratory Capacity in the first second (FEV1). Breathing reserve was calculated (BR). Oxygen consumption, absolute (VO2) and indexed (VO2i), percent predicted VO2 (%PVO2), expiratory minute volume (VE) and respiratory exchange ratio (RER) were obtained at anaerobic threshold (AT) and maximal exercise (Max). RESULTS: There were no significant differences between the BAV and C groups in age (14.6 ± 2.1 vs 15.8 ± 3.1(yr)), height (1.63 ± 0.1 vs 1.66 ± 0.12(m)) or weight (55.7 ± 15.1 vs 57.6 ± 13.2 (kg)). The BAV group had significantly decreased FVC (3.54 ± 0.84 vs 4.16 ± 1.03(L/min) p<0.05) and FEV1 (3.54 ± 0.84 vs 4.16 ± 1.03(L/min) p<0.02) compared to the C group. BAV group had a significant decrease in VO2 (1524 ± 466 vs 1876 ± 540 (ml/min) p<0.04), VO2i (28 ± 8 vs 33 ± 5 (ml/min/kg) p<0.04) and VE (35 ± 11 vs 42 ± 10 (L/min) p<0.02) at AT but not at Max. The %PVO2 was significantly decreased in the BAV group at AT (67 ± 19 vs 83 ± 18 (%) p<0.01) and Max (91 ± 24 vs 109 ± 17 (%) p<0.01). BR was significantly decreased in the BAV group (46 ± 6 vs 50 ± 6 (%) p<0.05) Max RER was not significantly different in BAV and C groups (1.19 ± 0.08 vs 1.19 ± 0.06). Significance was set at p< 0.05. CONCLUSION: BAV and C groups reached the same intensity of exercise reflected by the RER. BAV group had decreased pulmonary function, reflected by FVC and FEV1, with a decreased BR. BAV had decreased aerobic performance at AT and Max, reflected by the VO2, VO2i, and VE at AT and %PVO2 at AT and Max. These data suggest that a significant pulmonary function component contributes to the decreased aerobic performance in these BAV patients.