An 86-year-old man without documented coronary artery disease or conduction abnormalities at rest developed an episode of asystole following intravenous infusion of dipyridamole for 201Tl myocardial perfusion imaging and was reversed promptly after aminophylline injection. We reviewed the literature regarding the safety of this procedure and stressed the importance of close monitoring during the study, especially in patients receiving beta blockers, negative chronotropic or dromotropic agents.