Cardiac magnetic resonance imaging (CMR)-derived ejection fraction (EF) predicts adverse outcomes in repaired tetralogy of Fallot (rTOF) and drives timing of pulmonary valve replacement. Certain patient populations require sedation for successful CMR image acquisition. General anesthesia (GA) has been shown to depress EF and heart rate (HR) in animal models, however, its effect on congenital heart disease is unknown. A retrospective review was conducted of all CMR patients referred with rTOF between January 2011 and May 2019. The cohort was separated into GA and non-GA groups. Propensity score matching (PSM) adjusted for selection bias. A kernel matching algorithm was used to match subjects and the differences in mean treatment effect on the treated were computed for left ventricular (LV) and right ventricular (RV) EF, HR, and cardiac index (CI). 143 patients met criteria, 37 patients under GA (mean age 15 years, range 2–45, 59% male), and 106 patients without GA (mean age 21 years, range 10–53, 50% male). Unmatched analysis showed significant depression of LV EF (50 vs. 57%, p < 0.001) and RV EF (42 vs. 48%, p < 0.001) in the GA group compared to the non-GA group. There was no significant difference in HR or CI. After matching and PSM adjustment, the GA group had a significant decrease in LV EF (49 vs. 56%, p < 0.001), RV EF (41 vs. 48%, p < 0.001), CI (2728 vs. 3701 ml/min/m², p < 0.001), and HR (72 vs. 79 bpm, p = 0.04). General anesthesia with sevoflurane results in depressed CMR-derived EF.