Myocardial tissue characterization has been performed using various ultrasonic techniques, one of which is the cyclic variation of integrated backscatter, a method that analyzes the acoustic properties of the myocardium using backscattered radiofrequency signals to provide information about myocardial structure and function. Previous studies using prototype equipment have demonstrated a reduction in the cardiac cycle variation of integrated backscatter in various pathologic states. Recently, a commercially produced software package that allows online analysis of cyclic variation of integrated backscatter has been made available for testing by various investigators. To evaluate this new commercially produced software, we compared integrated backscatter results in three groups of patients: a control group; an end-stage cardiomyopathy group; and a heart transplant recipient group. Integrated backscatter of the septum and posterior walls in the parasternal long axis and 12, 3, 6, and 9 o'clock regions in the short axis was performed using a commercially produced program (Hewlett-Packard Sonos 1500). In the control group, the mean cyclic variation of integrated backscatter was 5.04 +/- 1.60 dB in the septum and did not significantly vary from the rest of the regions studied. In comparison, cyclic variation of integrated backscatter in every region studied was reduced in the cardiomyopathy and heart transplant groups. Intraobserver variability, interobserver variability, and reproducibility over a 3-month interval was found to be 6.5%, 5.7%, and 7.5%, respectively. These results indicate that: (1) online analysis of cardiac cyclic variation of integrated backscatter is possible utilizing commercially produced software; (2) results obtained are consistent with a low intraobserver and interobserver variability and are reproducible over time; and (3) as observed in the comparison between the transplant and control groups, this information may detect changes in cardiac structure even in the absence of changes in function. (ECHOCARDIOGRAPHY, Volume 13, May 1996)