The variability of left ventricular ejection fraction, normalized mean ejection rate and regional wall motion was evaluated from first pass quantitative radionuclide angiocardiograms obtained with a computerized multicrystal scintillation camera. Three radionuclide studies separated by an average of 4.3 days were obtained in each of 20 patients. Ejection fraction and ejection rate obtained on the first, second and third studies did not differ significantly. The mean (+/- standard deviation) variability of sequential ejection fraction measurement was 4.4 +/- 3.6 percent, and of sequential ejection rate was 0.56 +/- 0.47 sec(-1). Variations in measurements were not related to fluctuations in heart rate or blood pressure. Variability in ejection rate was significantly greater in patients with normal function than in those with abnormal function. Regional wall motion analysis was constant in 19 of 20 patients. Thus, sequential quantitative radionuclide angiocardiography allows reproducible serial assessment of left ventricular performance that can be performed with a low level of intrinsic variability.