OBJECTIVES: The purpose of this study was to assess the value of cardiovascular magnetic resonance (CMR)-determined graft flow and flow reserve in differentiating significant from non-significant vein graft disease. BACKGROUND: In patients after coronary artery bypass grafting (CABG), non-invasive testing may be helpful in the detection of recurrent graft disease. METHODS: Randomly selected patients (n = 21) scheduled for X-ray angiography because of recurrent chest complaints after CABG were included for evaluation of vein grafts (n = 40) by CMR. Three-dimensional contrast-enhanced CMR angiography was performed and followed by flow measurements at rest and during hyperemia in patent grafts only. Flow reserve was calculated when resting flow exceeded 20 ml/min. Analysis was based on four categories defined by X-ray angiography: occluded grafts (n = 3), grafts with stenosis >50% (n = 19), grafts with stenosis <50% with diseased graft run-off (n = 8), and grafts with stenosis >50% and normal run-off (n = 10). RESULTS: The CMR angiography demonstrated occlusion of three grafts. In nine of the 37 patent grafts, basal blood flow was <20 ml/min, all demonstrating significant stenosis at X-ray angiography. In grafts with resting flow >20 ml/min (n = 28), flow reserve significantly differed between grafts without stenosis and grafts with significant stenosis or with diseased run-off (2.5 ± 0.7 vs. 1.8 ± 0.9, p = 0.04). An algorithm combining basal volume flow <20 ml/min and graft flow reserve <2 had a sensitivity and specificity of 78% and 80% respectively for detecting grafts with significant stenosis or diseased run-off. CONCLUSIONS: This feasibility study showed that quantification of flow and flow reserve by CMR may serve as a non-invasive adjunct to differentiate between vein grafts without stenosis and grafts with significant stenosis or diseased ran-off.