For the evaluation of efficacy of cardiopulmonary exercise testing, we compared New York Heart Association functional class with peak oxygen consumption rate (VO₂peak) in 31 patients with severe mitral regurgitation who underwent mitral valve repair surgery. One year later, the VO₂peak values did not show significant improvement; however, the patients who had more than a mild degree of residual mitral regurgitation (n = 14) after 1 year of surgery had a VO₂peak value that was significantly decreased (from 22.7 ± 6.4 to 21.0 ± 6.3 ml/kg/min, p = 0.04). Patients with a higher preoperative VO₂peak value (≥18.5 ml/kg/min) had a significantly better New York Heart Association functional class 1 year after surgery than patients with a lower VO₂peak value (<18.5 ml/kg/min, p = 0.03).