The purpose of this study was to address the issue of 180 degrees versus 360 degrees data collection for left ventricular ejection fraction (LVEF) and left ventricular volume measurements using gated myocardial perfusion tomography (gMPT) and gated blood pool tomography (gBPT). Thirty patients with known coronary artery disease were injected in a random sequence with 925 MBq of technetium-99m tetrofosmin and, within 2 days, with 740 MBq of (99m)Tc-labelled human serum albumin. gMPT and gBPT were acquired using 360 degrees data collection and reconstructed by filtered backprojection using all the acquired projection images and separately using only projection images acquired from 45 degrees LPO to 45 degrees RAO. In order to have the same global count densities, the counts in the 360 degrees data set were redistributed using binomial deviates just before reconstruction. After reorientation along the left ventricular long axis, LVEF and left ventricular volumes were calculated using fully automatic algorithms. Twenty-eight patients also underwent planar radionuclide angiocardiography (PRNA) on the same day as the gBPT. For the gMPT studies, the correlation between 180 degrees data collection and 360 degrees data collection was excellent ( r>0.98). Bland-Altman analysis revealed small systematic and random differences (<6%) between 180 degrees and 360 degrees. For the gBPT studies, the correlation between 180 degrees data collection and 360 degrees data collection was very good ( r>0.93). However, Bland-Altman analysis revealed systematic differences of 26% and random differences of 17%. When PRNA was used as a reference, the best results were obtained with gMPT acquired using 180 degrees data, while the worst results were obtained with gBPT acquired using 180 degrees data. In conclusion, when evaluating LVEF and left ventricular volumes from gMPT, either 180 degrees or 360 degrees orbits can be used. However, 360 degrees data acquisition is recommended when evaluating LVEF and left ventricular volumes from gBPT.