To determine how pulmonary respiratory motion affected detection of pulmonary emboli, 11 dogs had routine lung scans and gated or cinematic perfusion images after autologous experimental pulmonary embolism. Six dogs had routine 6 view perfusion studies, plus end-inspiratory and end-expiratory gated perfusion studies performed with a physiologic synchronizer set to 80% threshold. Other dogs [5] had 3 view ungated and cinematic [post.[posterior], LPO [left posterior oblique], RPO [right posterior oblique] perfusion images. Cinematic studies were acquired by synchronizing a camera-computer system to the Harvard respirator that ventilated the dog. Before death all animals received i.v. India ink to outline pulmonary perfusion defects, and postmortem lung dissection verified sites of emboli. An ROC curve analysis of randomized perfusion studies showed that end inspiratory gated images yielded true-positive rates 5-10% higher than ungated images at any given false positive rate. Lesion detection by cinematic studies was comparable to detection by ungated images, but detection by end-expiratory images was worse. End-inspiratory gated imaging may be useful as an occasional adjunct to routine perfusion lung imaging.