Displacement of the atrioventricular (AV) plane toward the cardiac apex in systole was studied quantitatively by echocardiography in 37 patients with first-time acute myocardial infarction (MI) in order to evaluate left ventricular systolic function. The amplitude of AV plane displacement was recorded from the apex at four different sites corresponding to the septal, lateral, anterior, and posterior walls of the left ventricle from apical 4- and 2-chamber views. The patients had a decreased displacement of the AV plane compared with controls which was more pronounced at the sites of infarction. The mean value of the AV plane displacement (AV mean) correlated linearly with the left ventricular (LV) ejection fraction calculated by radionuclide angiography (r = 0.87, p less than 0.001, SEE = 6.2). An AV mean of 10 mm or more had a high sensitivity (95%) and specificity (82%) in defining a normal ejection fraction (greater than or equal to 50%). A high correlation coefficient was found between LV wall motion index and the AV plane displacement. Thus, in acute MI the LV function can be assessed noninvasively using AV plane displacement.