Background Left ventricular (LV) diastolic dysfunction contributes to signs and symptoms of clinical heart failure and may be related to prognosis in heart diseases. LV diastolic dysfunction is reported to be present in acute myocardial infarction (MI); however, little is known about the time course of changes in LV diastolic function and its relation to prognosis after acute MI. Methods and Results Two-dimensional and Doppler echocardiographic examinations were performed in 58 consecutive patients with first acute MI. The patients were studied serially within 1 hour and at days 5, 90, and 360 after arrival to the coronary care unit. LV diastolic function was assessed by Doppler measurements of transmitral and pulmonary venous flow. On the basis of mitral inflow, patients with MI were stratified at baseline to 3 LV diastolic filling patterns: normal, impaired relaxation, or pseudonormal/restrictive. Patients with MI were observed for development of congestive heart failure (Killip class >I) during hospitalization and for death during 1-year follow-up, and these complications were related to LV diastolic function. LV diastolic dysfunction was present in the very early phase of acute MI, with signs of impaired relaxation or restrictive LV filling dynamics in 38% and 24% of the patients, respectively, whereas 38% had normal LV filling characteristics. Impaired relaxation of the LV was most pronounced and found in 60% after 1-year follow-up. In-hospital congestive heart failure (Killip class >I) was found in 50% of the patients with initial impaired LV relaxation and in 71% of the patients with initially pseudonormal or restrictive LV filling dynamics, whereas patients with normal LV filling were free of heart failure. Patients with initial impaired relaxation and restrictive LV filling dynamics demonstrated a significant LV dilation during 1-year follow-up. Patients with initial pseudonormal/restrictive LV filling pattern were more frequently readmitted to the hospital for heart failure and had significant higher New York Heart Association class score compared with patients with normal or impaired relaxation during follow-up. Cardiac death was (n = 6) only observed in patients with pseudonormal or restrictive LV filling pattern. In a multivariate stepwise regression analysis, mitral E deceleration time ≤140 ms and age were identified as independent variables related to development of in-hospital congestive heart failure and cardiac death during 12 months of follow-up. Conclusions LV diastolic dysfunction is present in the very early phase of MI. LV remodeling and development of in-hospital congestive heart failure appear in patients with very early signs of LV diastolic dysfunction. Furthermore, mitral E deceleration time ≤140 ms best identified patients at risk of development of in-hospital congestive heart failure and cardiac death after MI. (Am Heart J 1999;137:910-8.)