This study aimed to evaluate CFR by assessing blood flow in the coronary sinus and systemic endothelial function measured by FMD of the brachial artery in an open prospective study of 10 control subjects and 10 patients (ages, 15–25 years) who have undergone surgical TOF repair. Reduced ventricular function, impaired exercise capacity, and ventricular arrhythmia have been proposed as risk factors for sudden cardiac death after surgical repair of TOF. Some of this may be related to impaired myocardial perfusion. A 3.0T GE Signa Excite scanner was used to achieve phase-contrast, velocity-encoding cine magnetic resonance imaging in the coronary sinus before and during infusion with adenosine (0.14 mg/kg/min). FMD was measured in the brachial artery before arterial occlusion and 5 min afterward. The TOF group demonstrated significantly higher volumetric blood flow in the coronary sinus (282 ± 63 ml/min) than the normal control subjects at rest (184 ± 57 ml/min) (P = 0.006). During adenosine infusion, this difference disappeared. The CFR was 2.00 ± 0.43 in the control group and 1.19 ± 0.34 in the TOF group (P = 0.002). No correlation between FMD and CFR was observed in the study group (r _s = 0.61, n = 8, P = 0.15). This study showed a reduced CFR due to a higher blood flow of the subject at rest in the TOF group. This reduced CFR may disable a normal adaptation to increased oxygen demand during exercise and increase myocardial vulnerability to reduced blood supply postoperatively for TOF patients with coronary heart disease.