Manual measurement of left ventricular volume from 3D echocardiographs is time consuming, and there is a clinical need for automatic methods. We describe a semiautomatic method which uses a 3D image gradient operator and a short-axis boundary detector. Six patients with cardiomyopathy were studied using 3D echocardiography and the images were analysed to measure the repeatability of measurement by the semi-automated method, and used to compare measurements of stroke volume and ejection fraction with manual measurements. Within-patient standard deviations of the semi-automated method were 14.6% and 16.4% of the group mean end diastolic and end systolic volumes respectively, and were significantly less than the between-patient standard deviations. No differences between the semi-automated method and the manual method were found for the measurements of ejection fractions or of stroke volumes