Depressed left ventricular performance is often observed after mitral valve replacement for mitral regurgitation and is generally attributed to increased impedance to left ventricular ejection. We analyzed preoperative and postoperative catheterization data in 10 of 18 patients who underwent mitral reconstruction with preservation of the native valves and found a significant (p less than 0.05) fall in left ventricular end-diastolic volume index (from 143 +/- 39 to 84 +/- 21 ml/m2) and end-systolic volume index (from 50 +/- 24 to 32 +/- 12 ml/m2), with no significant change in ejection fraction (0.66 +/- 0.1 versus 0.62 +/- 0.1). These findings contrast with studies reported by others in comparable patients who had mitral valve replacement with no improvement in volume indices and a decline in ejection fraction postoperatively. We suggest that some of the left ventricular dysfunction observed after mitral replacement may be due simply to excision of the native valve. Mitral repair retains the tethering effect of chordal attachments and may thus prevent postoperative left ventricular dilatation and moderate the increase in wall stress that results from increased impedance to left ventricular ejection.