The persistence of moderate ischemic mitral regurgitation (IMR) after isolated coronary artery bypass graft surgery is an important independent predictor of long-term mortality. The aim of the present study was to identify predictors of postoperative improvement in moderate IMR in patients with ischemic heart disease undergoing elective isolated coronary artery bypass graft surgery. The study population consisted of 135 patients with ischemic heart disease (age, 65+/-9 years; 81% male) and moderate IMR undergoing isolated coronary artery bypass graft surgery. Fourteen patients died before the 12-month follow-up echocardiography and were excluded. At the 12-month follow-up, 57 patients showed no or mild IMR (improvement group), whereas 64 patients failed to improve (failure group). Before coronary artery bypass graft surgery, the improvement group had significantly more viable myocardium and less dyssynchrony between papillary muscles than the failure group (P<0.001). All other preoperative parameters were similar in both groups. Large extent (> or =5 segments) of viable myocardium (odds ratio, 1.45; 95% confidence interval, 1.22 to 1.89; P<0.001) and absence (<60 ms) of dyssynchrony (odds ratio, 1.49; 95% confidence interval, 1.29 to 1.72; P<0.001) were independently associated with improvement in IMR. The majority (93%) of patients with viable myocardium and an absence of dyssynchrony showed an improvement in IMR. In contrast, only 34% and 18% of patients with dyssynchrony and nonviable myocardium, respectively, showed an improvement in IMR, whereas 32% and 49%, respectively, of these patients showed worsening of IMR (P<0.001). Reliable improvement in moderate IMR by isolated coronary artery bypass graft surgery was observed only in patients with concomitant presence of viable myocardium and absence of dyssynchrony between papillary muscles.