Acute myocardial ischemia and chronic myocardial infarction may be recognized with ultrasound tissue characterization techniques because of myocardial acoustic changes caused by reduced perfusion and/or collagen deposition. Our purpose was to study the acoustic properties of recent myocardial infarction when the predominating pathologic finding was myocardial edema and leukocytic infiltration. We used a new quantitative backscatter imaging system to study 18 patients 9 +/- 5 days after myocardial infarction (eight patients with anteroseptal myocardial infarction and 10 with inferior myocardial infarction) and 20 normal subjects. The cyclic variation of relative integrated backscatter (end-diastolic minus end-systolic) was calculated from on-line measurements. Standard parasternal long- and short-axis and apical four- and two-chamber views were obtained. In the anteroseptal myocardial infarction group, the cyclic variation of relative integrated backscatter was lower in the septum (1.5 +/- 1.6 dB) than in the posteroinferior wall (3.2 +/- 1.2 dB); however, the sample size of only three patients (of eight patients imaged) in the latter group prevented statistical comparison. The cyclic variation of relative integrated backscatter in the infarcted septum was less than the measurement obtained in the septum of the control group (4.3 +/- 2.4 dB, p less than 0.05). In the inferior infarction group, the cyclic variation of integrated backscatter in the posteroinferior wall (1.8 +/- 1.7 dB) was not significantly different from the measurement obtained in the septum (3.7 +/- 3.6 dB); however, the cyclic variation in the posteroinferior wall was significantly less than that obtained in the control group posteroinferior wall (5.7 +/- 1.7 dB, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)