Background and objectives Diagnostic availability of stress rest 99mTc sestamibi single photon emission computed tomography (SPECT) in patients with atrial fbrillation has not been studied. The aim of this study was to assess the usefulness of 99mTc sestamibi SPECT for detection of coronary artery disease (CAD) in patients with atrial fibrillation as compared to those with regular sinus rhythm. Method This study included 26 patients with atrial fibrillation and 256 control subjects with regular sinus rhythm. We excluded previous myocardial infarction history, previous diagnosed CAD, ejection fraction < 50% and regional wall motion abnormality by echocardiogram. All patients underwent adenosine 99mTc sestamibi SPECT and coronary angiogram. The SPECT study was considered abnormal if the summed stress score (SSS) is 3 or greater. Criteria for significant CAD was defined as ���70% stenosis in any of the three major epicardial coronary arteries. Result The basic characteristics were not significantly different between two groups. In normal SPECT study group (n=84), 43 (55.1%) of 84 patients with regular sinus rhythm and 4 (66.7%) of 6 patients with atrial fibrillation were not found CAD by coronary angiogram. In abnormal SPECT study group (n=198), 74 (42.6%) of 178 patients with regular sinus rhythm and 8 (40%) of 20 patients with atrial fibrillation were detected CAD. There were no significant diagnostic differences between regular sinus rhythm and atrial fibrillation group. Conclusion Detectable availablity by 99mTc sestamibi SPECT in atrial fibrillation patients is not inferior to that in RSR patients.