Noninvasive tests have proven unsatisfactory in cardiac allograft vasculopathy (CAV) diagnosis. We assessed coronary flow reserve (CFR) by contrast-enhanced transthoracic echocardiography (CE-TTE) in heart transplantation (HT). CFR was assessed in the left anterior descending coronary artery in 73 HT recipients (59 male, aged 50+/-12 years at HT), at 8+/-4.5 years post-HT. CFR measurements were taken blindly from coronary angiographies. CFR cut points were the standard value of <or=2 and those defined by receiver operating characteristics (ROC) curve analysis. CFR was lower in patients with CAV (2.3+/-0.7 vs. 3.2+/-0.5, p<0.0001). The <or=2 cut point was 100% specific and 38% sensitive. The <or=2.7 cut point, optimal by ROC analysis, was 87% specific and 82% sensitive. Accuracy rose from 71% with the standard<or=2 cut point to 85% with the optimal cut point of <or=2.7. CFR by CE-TTE may offer promise as a novel, easily repeatable and accurate noninvasive tool in CAV detection. However, further longitudinal studies in larger patient cohorts are warranted before widespread adoption can be advocated.