Mitral regurgitation (MR) complicating acute myocardial infarction (AMI) is associated with increased mortality. The prognostic significance of only mild MR detected by echocardiography in patients with AMI is unknown. This study assessed the long-term risk associated with mild MR detected by color Doppler echocardiography within the first 48 hours of admission in 417 consecutive patients with AMI. No MR was detected in 271 patients (65%), mild MR was seen in 121 patients (29%), and moderate or severe MR was noted in 25 patients (6%). One-year mortality rates were 4.8%, 12.4%, and 24%, respectively (p<0.001). Multivariate analysis revealed that mild MR was independently associated with increased 1-year mortality (p<0.05) after adjustment for age, gender, previous myocardial infarction, diabetes mellitus, systemic hypertension, Killip grade > or =2 on admission, and left ventricular ejection fraction < or =40%. The hazard ratio for 1-year mortality was 2.31 (95% confidence interval 1.03 to 5.20) for mild MR and 2.85 (95% confidence interval 0.95 to 8.51) for moderate or severe MR. Thus, mild MR detected by color Doppler echocardiography within the first 2 days of admission in patients with AMI is a significant independent risk predictor for 1-year all-cause mortality.