BACKGROUND: After reports of cardiac impairment caused by mitral annuloplasty with rigid rings, several prosthetic rings with semi-rigidity were introduced. The influence of semi-rigid rings on postoperative cardiac function remains unknown. This study compared postoperative cardiac function between patients receiving a semi-rigid prosthetic ring and those receiving a flexible ring or band. METHODS AND RESULTS: Transthoracic echocardiographic data of 305 patients who underwent mitral valve repair for degenerative mitral regurgitation (227 patients receiving a semi-rigid ring and 78 receiving a flexible ring or band) were retrospectively reviewed. The imbalance in the preoperative characteristics between groups was adjusted with propensity score matching. Left ventricular ejection fraction, end-diastolic dimension, and end-systolic dimension were compared at 1 week, 6 months, and 1 year after surgery. Propensity score matching yielded 68 matched pairs of patients for whom there were few group differences in preoperative covariates. Between patients receiving a semi-rigid ring and those receiving a flexible ring or band in the propensity-matched cohorts, there were no significant differences in ejection fraction (P=0.322), end-diastolic dimension (P=0.576), or end-systolic dimension (P=0.567). CONCLUSIONS: There was little difference in the influence on postoperative cardiac function between semi-rigid rings and flexible rings or bands.