Electrocardiogram gated cardiac computed tomography (CT) was performed to evaluate the usefulness in the measurement of left ventricular volume and left ventricular wall thickness in 25 patients; five with angina pectoris, five with old myocardial infarction, eight with hypertrophic cardiomyopathy, four with dilated cardiomyopathy, and three healthy men. The left ventricular volume was calculated as the sum of the volume of each slice, which was area times thickness of the slice. The left ventricular wall thickness was measured in reconstructed short-axis view at the level of the mitral valve and papillary muscle. The left ventricular volume and left ventricular wall thickness determined by CT were compared with that by left ventriculography (LVG), and that by two-dimensional echocardiography (2 DE), respectively. The following results were obtained. There were good relationships between left ventricular volume, end-diastolic volume, end-systolic volume, ejection fraction by CT and those by LVG, but left ventricular volume by CT was smaller by about 20% than that by LVG. In the measurement of stroke volume, no relationship was recognized between CT and LVG. Concerning the measurement of left ventricular wall thickness, more available figures were obtained by CT than by 2 DE, particularly at the apical region, lateral wall, and posterior wall. In the other segments of the left ventricle, CT was also more suitable for the measurement of the wall thickness. Interventricular septal thickness was correlated between reconstructed short-axis view of CT (Y) and transverse view of CT (X), and the equations Y = 0.66X + 2.13 (r = 0.79) at the mitral valve level, and Y = 0.56X + 3.00 (r = 0.81) at the papillary muscle level were obtained. Therefore, reconstructed short-axis view should be used for the measurement of the left ventricular wall thickness not to overestimate the thickness.