Background: Impaired coronary vasodilation to both endothelial-dependent and endothelial-independent stimuli have been associated with atherosclerosis. Direct measurement of coronary vasodilation using x-ray angiography or intravascular ultrasound is invasive and, thus, not appropriate for asymptomatic patients or for serial follow-up. In this study, high-resolution coronary cardiovascular magnetic resonance (CMR) was used to investigate the vasodilatory response to nitroglycerine (NTG) of asymptomatic patients at high risk for CAD. Methods: A total of 46 asymptomatic subjects were studied: 13 high-risk patients [8 with diabetes mellitus (DM), 5 with end stage renal disease (ESRD)] and 33 age-matched controls. Long-axis and cross-sectional coronary artery images were acquired pre-and 5 minutes post-sublingual NTG using a sub-mm-resolution multi-slice spiral coronary CMR sequence. Coronary cross sectional area (CSA) was measured on pre-and post-NTG images and % coronary vasodilation was calculated. Results: Patients with DM and ESRD had impaired coronary vasodilation to NTG compared to age-matched controls (17.8 +/- 7.3% vs. 25.6 +/- 7.1%, p = 0.002). This remained significant for ESRD patients alone (14.8 +/- 7.7% vs. 25.6 +/- 7.1%, p = 0.003) and for DM patients alone (19.8 +/- 6.3% vs. 25.6 +/- 7.1%, p = 0.049), with a non-significant trend toward greater impairment in the ESRD vs. DM patients (14.8 +/- 7.7% vs. 19.8 +/- 6.3%, p = 0.23). Conclusion: Noninvasive coronary CMR demonstrates impairment of coronary vasodilation to NTG in high-risk patients with DM and ESRD. This may provide a functional indicator of subclinical atherosclerosis and warrants clinical follow up to determine prognostic significance.