Several controlled trials on the thrombolytic treatment of acute myocardial infarction (AMI) have failed to demonstrate that thrombolysis has a simultaneous positive effect on left ventricular function and survival. One explanation may be that spontaneous changes in left ventricular function occurred during the progression of AMI in control patients. The aim of this study was to evaluate the spontaneous evolution of left ventricular ejection fraction (LVEF) and its prognostic influence on early (1 month) and late (1 year) mortality in patients with AMI. We studied 216 patients admitted to our CCU within 24 h of the onset of symptoms. LVEF was determined by radionuclide ventriculography on admission (RNV1) and at the end of the necrotic phase (RNV2). Fourteen patients died before RNV2. On the basis of LVEF values at RNV1, the remaining 202 patients were divided into two groups: those with a normal LVEF (> or = 55%), and those with an abnormal LVEF (< 55%). Among patients with a normal LVEF at RNV1 (64 patients), a significant increase (> 12%) in LVEF at RNV2 was observed in 12.5%, a significant decrease (> 12%) in 12.5% and no change at all in 75%. All of these patients survived, regardless of the evolution of LVEF. In patients with an abnormal LVEF at RNV1 (138) a significant increase (> 5%) in LVEF at RNV2 was observed in 72.5%, a significant decrease (> 5%) in 6.5% and no change at all in 21%.(ABSTRACT TRUNCATED AT 250 WORDS)