We evaluated postinfarction myocardial function in rats and determined echocardiographic criteria for congestive heart failure (CHF) using high performance echocardiography. Extensive myocardial infarction (MI) was induced in rats by left coronary occlusion. Sham-operated animals served as controls. Five weeks later, high-frame rate ( approximately 200 Hz), fully digitized, shallow-focus (10-25 mm), two-dimensional, M-mode and Doppler echocardiography was performed. A J-tree cluster analysis was performed using parameters indicative of CHF. Reproducibility was examined. The cluster analysis joined the animals into one Sham and two MI clusters. One of the MI clusters had clinical characteristics of CHF and elevated left ventricular end diastolic pressure. Among the echocardiographic variables, only posterior wall shortening velocity separated the failing and nonfailing MI clusters. We conclude that, by high frame rate echocardiography, it is possible to obtain high- quality recordings in rats. It is feasible to distinguish MI rats with CHF due to myocardial dysfunction from those without failure and to perform longitudinal studies on myocardial function.