To investigate the natural history of regional dyssynergy and left ventricular size after myocardial infarction, 57 patients with a first Q wave myocardial infarction (18 anterior, 35 inferior, and four apical by echocardiography) were studied by two-dimensional echocardiography and compared with 30 control patients. Measurements from the echocardiograms were used to construct maps of the left ventricular endocardial surface from which the endocardial surface area index (ESAi) and the percent of the endocardial surface area involved by abnormal wall motion (%AWM) were calculated. The maps from entry and 3-month echocardiograms were used to classify patients based on changes in ESAi and abnormal wall motion. Two subgroups of patients were identified at entry--those with a normal ESAi (group 1, n = 50) and those with an increased ESAi (group 2, n = 7). Group 1 patients was subdivided at 3 months by changes occurring in ESAi (1A, 5% increase [n = 19]; 1B, no change [n = 23]; 1C, 5% decrease [n = 8]). The increase in ESAi (64.9 +/- 5.2 to 75.4 +/- 7.5 cm2/m2, p less than 0.0001) in group 1A was associated with global ventricular dilatation (n = 11) and clinically silent infarct extension (n = 8). Groups 1B and 1C were composed predominantly of patients with inferior infarctions, and all exhibited either no change or a significant decrease in infarct size (infarct regression). Group 2 patients demonstrated a continued increase in ESAi by 3 months (88.2 +/- 10.0 to 101.4 +/- 15.5 cm2/m2, p less than 0.007). This group comprised only patients with anterior infarctions, and all exhibited infarct expansion at the left ventricular apex. The changes in left ventricular size and functional infarct size are heterogeneous after acute myocardial infarction and relate to the initial endocardial surface area, infarct location, and functional infarct size.