['Misregistration of cardiac PET/CT data can lead to misinterpretation of regional myocardial perfusion. However, the effect of misregistration on the quantification of myocardial blood flow (MBF) has not been studied.', 'Cardiac (82)Rb-PET/CT scans of 10 patients with normal regional myocardial perfusion were analyzed. Realignment was done for the baseline and stress PET/CT images as necessary, and MBF was obtained from dynamic data. Then, the stress images were misregistered by 5 mm along the x-axis (left) and z-axis (cranial) and again by 10 mm. A 10-mm misregistration in the opposite direction (-10 mm along the x-axis [right] and z-axis [caudal]) was also tested. Stress MBF was recalculated for 5-, 10-, and -10-mm misregistrations.', 'Stress MBF of the left ventricle decreased by 10% ± 6% (P = 0.005) after 5-mm misregistration and by 24% ± 15% (P = 0.001) after 10-mm misregistration. In descending order, the most important stress MBF changes occurred in the anterior (39% ± 9%), lateral (34% ± 9%), apical (20% ± 16%), inferior (12% ± 10%), and septal (10% ± 12%) walls after 10-mm misregistration. Lesser changes were observed after 5-mm misregistration, with the same wall distribution. In contrast, -10-mm misregistration increased global MBF by 9% ± 6% (P = 0.004). In descending order, the overestimation of estimated MBF after -10-mm misregistration occurred in the lateral (15% ± 8%), apical (15% ± 18%), anterior (9% ± 5%), and inferior (9% ± 11%) walls.'] Does cardiac PET/CT misregistration cause significant changes in estimated myocardial blood flow?