This study was designed to determine whether attenuation of ultrasound by myocardium is potentially useful in detecting and quantifying infarction. Accordingly, we analyzed 44 regions of myocardium from 11 dogs 4-10 weeks after coronary occlusion. Attenuation of ultrasound in each region was assessed by transmitting a broadband pulse through the tissue in vitro and carefully gating the appropriate pulse into a spectrum analyzer for Fourier analysis (frequency range, 2-9.5 MHz). An ultrasonic index of attenuation was derived from the slope of the best-fit line relating attenuation and frequency obtained from the Fourier transform. Acquisition of ultrasonic data was improved with the use of a specially designed small diameter receiving transducer. Myocardial creatine kinase content was assayed in each region to provide an independent index of regional injury. Results obtained from ultrasonic and biochemical analyses correlated with a correlation coefficient between the two of 0.80 in 24 regions of myocardium from the six dogs studied 4-5 weeks after infarction, and 0.72 in 20 regions from the five dogs studied 9-11 weeks after infarction. These findings indicate that regional infarction is associated with quantitative changes in ultrasonic attenuation.