It has been shown that cineangiographic measurement of the mean rate of circumferential fiber shortening (mean VCF) at the minor left ventricular equator is a reliable method for evaluating the mechanics of cardiac performance. Since fiber shortening can be derived from the echocardiogram, we sought to validate the measurement of mean VCFby this noninvasive technic in patients studied by both methods. In 15 patients considered to have normal left ventricular function, the average mean VCFdetermined by ultrasound was 1.29 ± 0.23 circumferences/sec, while in the 13 patients with reduced left ventricular performance this value was 0.75 ± 0.16 circumferences/sec (P< 0.001). Values of mean VCFby the two technics were similar and separated normal from abnormal ventricular function in 27 of 28 patients. The average mean velocity of posterior wall motion was 4.7 ± 1.1 cm/sec in normal patients and 3.9 ± 1.3 cm/sec in abnormals, but posterior wall velocities did not correlate well with either ultrasound or cineangiographic determinations of mean VCF. Ejection fraction calculated from ultrasound measurements correlated significantly with the ejection fraction calculated by cineangiography (r = 0.83,P< 0.0001). The ejection fraction and mean VCF, as determined by ultrasound in the 28 patients, correlated well (r = 0.92,P< 0.0001), but there were six discordant points.From these studies we conclude that the ultrasound determination of mean VCFis a valid method for distinguishing normal from abnormal myocardial performance of the left ventricle. These data also support the use of ultrasound in determining ejection fraction. Estimation of posterior wall velocity, although perhaps useful in the serial study of the same patient, seems limited in its ability to assess cardiac performance accurately.