A geometric method of measuring absolute left ventricular volumes from gated blood-pool studies obtained in a single-plane modified left anterior oblique view was evaluated prospectively in 30 patients who also underwent single-plane contrast ventriculography. The gated studies used a 30° straight-bore slant-hole collimator with the holes slanted caudally. Left ventricular end-diastolic volume was calculated using the area-length method, with semiautomatic definition of the left ventricular region of interest and the maximum length of the left ventricle. Ejection fraction was determined from the left ventricular time/activity curve. The left ventricular end-systolic volume was derived using the end-diastolic volume and ejection fraction. Correlation coefficients between the two methods were 0.93 for end-diastolic volume, 0.95 for end-systolic volume, and 0.91 for ejection fraction. This method provided accurate and highly reproducible measurements of actual left ventricular volumes and was easily applicable in routine clinical studies.