Serial simultaneous M mode echocardiograms, phonocardiograms, and apexcardiograms were recorded and digitised in 20 patients with a first myocardial infarction immediately after and two, three, seven, and 56 days after hospital admission. Left ventricular maximum and minimum dimensions, normalised maximum rate of change of dimension during systole and diastole, and three previously defined indices of the coordination of left ventricular wall motion were measured. Incoordinate left ventricular wall motion was detected in all patients but was more pronounced in those with an anterior infarction (15) than in those with an inferior infarction (5). Although on the first three days after admission patients with heart failure (7) were indistinguishable echocardiographically from those without (13), differences became apparent later with an increase in left ventricular dimension and more pronounced evidence of incoordination in those with heart failure. In the first two days after admission patients with full thickness infarcts (14) were indistinguishable echocardiographically from those with partial thickness infarcts (6) despite the former being of much larger size as judged by the measurement of cardiac enzyme activity. Abnormal indices of coordination reverted to normal with time in patients with partial thickness infarctions, whereas only partial reversion of these indices occurred in those with full thickness infarctions. The use of digitised M mode echocardiograms is a sensitive means of detecting and following the evolution of incoordinate left ventricular wall motion in patients with an acute myocardial infarction whatever the position, type, or size of the infarct. Incoordination so detected is, however, quantitatively unrelated to infarct type or size or to the clinical state of the patient.