We assessed the relation between systemic endothelial dysfunction abnormalities (brachial artery flow-mediated dilation) and myocardial perfusion abnormalities (single-photon emission computed tomography) in 41 patients who had cardiac syndrome X. Eighteen patients had normal perfusion scans and 18 had transient perfusion defects. Reverse redistribution was found in 5 patients. Patients who had myocardial perfusion defects had significantly lower flow-mediated dilation values (1.8%) than patients who had normal single-photon emission computed tomograms (3.9%, p = 0.012). Preserved systemic endothelial function appears to rule out the occurrence of transient single-photon emission computed tomographic defects in patients who have cardiac syndrome X.