The purpose of this study was to determine the use of ultrasonic tissue characterization (UTC) for the diagnosis of acute myocardial infarction (AMI). Real-time UTC and conventional 2-dimensional echocardiography were performed with a research prototype and commercially available ultrasonoscope, respectively, in 60 consecutive patients with suspected AMI. Diagnosis of AMI was documented by the presence of 2 of the 3 following clinical criteria: (1) typical history, (2) characteristic electrocardiographic changes, and (3) an increase in creatine phosphokinase-MB. Myocardial infarction was present in 24 of 60 patients and absent in 36 of 60 patients. Tissue characterization correctly diagnosed the presence of myocardial infarction in 22 of 24 patients and the absence in 33 of 36 patients. Two-dimensional echocardiography detected the presence of myocardial infarction in 21 of 24 patients and the absence in 34 of 36 patients. UTC had 2 false-negative and 3 false-positive studies, all in the region of apical infarcts. Two-dimensional echocardiography had 3 false-negative studies in patients with non-Q-wave myocardial infarction and 2 false-positive studies in patients with complete left bundle branch block. Both techniques had a comparable sensitivity, specificity, and accuracy.