Ultrasonic sector-scan images can delineate the entire circumference of the canine left ventricle in vitro. This study was undertaken to (1) assess the accuracy of sector scanning for estimating canine left ventricular volume in vitro compared to volume estimates by M-mode echo in the same hearts and (2) determine the optimal techniques for estimating left ventricular volume with sector scanning. 16 volumes (1 volume from 8 hearts and 2 volumes from 4 hearts) were estimated by obtaining sector-scan images from orthogonal long-axis, short-axis and apical views. The sector-scan volumes were calculated by single and biplane area-length methods, as well as biplane Simpson’s rule methods, and compared to measured left ventricular volumes. M-mode echo volumes were calculated by cubing the mid-ventricular minor-axis diameter. Sector-scan views containing a long-axis dimension plus the short-axis dimension of the left ventricle had a high correlation with true left ventricular volume while sector-scan views not containing a long-axis view showed only a fair correlation with volume. M-mode echo produced a poor estimate of the true left ventricular volume. It is concluded that (1) sector scanning can provide highly accurate in vitro volume estimates of canine left ventricles which is superior to estimates derived by M-mode echocardiographic methods and (2) the optimal sector-scan views for estimating left ventricular volume are those that make the fewest assumptions about left ventricular geometry and have the greatest amount of dimensional information.