A left ventricular pressure volume loop (PV loop) is useful not only in evaluating cardiac function, but also in predicting the postoperative hemodynamic state. There are two methods available for the intraoperative measurement of a PV loop: a conductance catheter and two-dimensional echocardiography. Although the accuracy of conductance catheter is well established for the measurement of ventricular volume, however, the accuracy of echocardiography remains controversy. This paper describes the relationship of parameters including volumes and Emax calculated with each method. Six patients who underwent open heart surgery were included in this study. Comparison of the absolute volumes at four points at the corners of the PV loop showed a Pearson's correlation coefficient of 0.62 (p-value < 0.01). In comparison with the relative volumes at four points which reflect the preoperative to postoperative change ratio, the correlation coefficient was 0.74 (p < 0.01). The correlation coefficients were 0.76 (p = 0.16) and 0.63 (p = 0.29) for the ratio of the end-diastolic and end-systolic volume respectively. Each preload-varying "Emax: out" (r = 0.84, p < 0.01) were highly correlated. As a predictor of cardiac oxygen consumption, each PVA (r = 0.84, p < 0.01) was highly correlated. We conclude that the measurement of left ventricular volume using two-dimensional echocardiography is as reliable as the conductance catheter.