This study was aimed at assessing the value of preoperative forward ejection fraction (FEF) and corrected forward ejection fraction (CFEF) as an index of postoperative myocardial function. Utilizing 34 patients with mitral regurgitation, usefulness of the preoperative FEF and CFEF was evaluated with special reference to incidence of postoperative low output syndrome (LOS) and improvement in the New York Heart Association (NYHA) classification, comparing other indices of left ventricular function such as cardiac index (CI), stroke index (SI), left ventricular end-diastolic volume index (LVEDVI) and left ventricular end-systolic volume index (LVESVI). There was a significant correlation between FEF and CI, SI, LVEDVI or LVESVI, and between CFEF and CI, SI, LVEDVI or LVESVI. The FEF and CFEF, however, were better indicators for predicting the occurrence of postoperative LOS than EF. Postoperative improvements in the NYHA classification were parallel to that of the FEF and CFEF changes, but did not coincide with that of the EF. Based on these findings, it is concluded that FEF and CFEF are more useful indicators than EF for evaluation of left ventricular myocardial performance in patients with mitral regurgitation.