OBJECTIVES: The purpose of this study was to assess myocardial blood flow (MBF) and flow reserve in systemic right ventricles (RV) in long-term survivors of the Mustard operation. BACKGROUND: There is a high prevalence of systemic RV dysfunction and impaired exercise performance in long-term survivors of the Mustard operation. A mismatch between myocardial blood supply and systemic ventricular work demand has been proposed as a potential mechanism. METHODS: We assessed MBF at rest and during intravenous adenosine hyperemia in 11 long-term survivors of a Mustard repair (age 18 ± 5 years, median age at repair 0.7 years, follow-up after repair 17 ± 5 years) and 13 healthy control subjects (age 23 ± 7 years), using N-13 ammonia and positron emission tomography imaging. RESULTS: There was no difference in basal MBF between the systemic RV of survivors of the Mustard operation and the systemic left ventricle (LV) of healthy control subjects (0.80 ± 0.19 vs. 0.74 ± 0.15 ml/g/min, respectively, p = NS). However, the hyperemic flows were significantly lower in systemic RVs than they were in systemic LVs (2.34 ± 0.0.69 vs. 3.44 ± 0.62 ml/g/min respectively, p ≤ 0.01). As a result, myocardial flow reserve was lower in systemic RVs than it was in systemic LVs (2.93 ± 0.63 vs. 4.74 ± 1.09, respectively, p ≤ 0.01). CONCLUSIONS: Myocardial flow reserve is impaired in systemic RVs in survivors of the Mustard operation. This may contribute to systemic ventricular dysfunction in these patients.