Mitral regurgitation (MR) after acute myocardial infarction (AMI) is an important prognostic factor. Although its mechanisms are still debated, ventricular remodeling probably plays an important role. Because myocardial viability (MV) in the infarct zone reduces infarct expansion and ventricular remodeling, it is also possible that its presence counteracts the development of mitral regurgitation in infarcted patients. To evaluate this issue 191 patients with uncomplicated AMI, wall motion abnormalities (akinesis) and semiquantitative evaluation of MR were retrospectively selected from those consecutively examined at our echo-laboratory to evaluate MV using low-dose dobutamine echocardiography (DbE). Follow-up evaluation was performed at 30+/-13 months. Seventy-nine patients had no MR; 86 patients had grade 1 MR, 11 patients had grade 2 MR, nine patients had grade 3 MR, and six patients had grade 4 MR. Patients with significant MR (>grade 1) were older (63+/-7 vs. 59+/-10 years, P=0.03), had lower reduction of RWMSI (DeltaRWMSI) during DbE (0.08+/-0.11 vs. 0.22+/-0.28, P=0.01), more stenotic vessels at coronary angiography (2.35+/-0.93 vs. 1.67+/-1.12, P=0.01), and more frequently had anterior-inferior AMI (P<0.0001); they also had a non-significant tendency to higher RWMSI (2.04+/-0.38 vs. 1.92+/-0.28, P=0.06). In a multivariate regression analysis, DeltaRWMSI proved to be significantly related to the grade of MR (P=0.02). Eighteen patients died during follow-up. Death was more frequent in patients with MR (10/165 vs. 8/26, P=0.0003). At multivariate stepwise Cox regression analysis both the extent of ventricular dysfunction and the presence of MR were significantly related to mortality (P<0.0001 and P=0.01, respectively); DeltaRWMSI showed a non-significant tendency to influence mortality (P=0.09). When MR was excluded from the multivariate analysis, DeltaRWMSI remained significantly related to mortality (P=0.05). In conclusion our study suggests that the presence of MV in infarcted patients influences the development of MR. This reduction of MR may be one of the mechanisms by which MV affects mortality after AMI and should be considered in all studies that evaluate MV after myocardial infarction.