Assessment of left ventricular (LV) function is crucial in the immediate postinfarction period. The authors evaluated the clinical applicability of the Doppler-derived myocardial performance index (MPI, defined as the sum of isovolumic contraction and relaxation times divided by LV ejection time) in patients with acute myocardial infarction (AMI) as to whether this index reflects the severity of LV dysfunction in this subgroup of patients. Post-AMI patients (n = 33) were compared with age- and sex-matched healthy subjects (n = 35). Within 24 hours of the AMI and 1 month thereafter, patients underwent 2D and Doppler echocardiography. Patients were divided into group A (Killip Class I, n = 22) and group B (Killip Class II-III, n = 11). The authors measured the LV ejection fraction (EF), diastolic indices (transmitral E and A waves, E/A ratio, deceleration time [DT], isovolumic contraction time [IVCT], isovolumic relaxation time [IVRT], MPI, LV end-systolic and end-diastolic volume indices [ESVi and EDVi] and wall motion score index [WMSi]). One-year mortality was also assessed. There was no significant difference concerning E and A waves, E/A ratio, and IVRT between the 2 groups. There were highly statistical differences at day 1 for EF (59.3 +/- 6.7% vs 36.8 +/- 4.5%, p<0.0001), DT (0.160 +/- 0.030 sec vs 0.127 +/- 0.022, p<0.005), MPI (0.344 +/- 0.084 vs 0.686 +/- 0.120, p<0.0001), ESVi (28.4 +/- 3.9 mL/m2 vs 46.2 +/- 8.4, p<0.001), and WMSi (1.58 +/- 0.06 vs 1.88 +/- 0.35, p=0.05), which persisted after 1 month. One-year mortality was significantly (0 vs 27.3%, p<0.01) lower in group A patients. This study shows that the MPI, reliably indicated LV dysfunction post-AMI, significantly correlated with clinically determined functional class, and possibly has some prognostic implication.