Left ventricular (LV) diastolic dysfunction is associated with poor outcomes after tetralogy of Fallot (TOF) repair, although its cause is not known, and its relation to right ventricular (RV) performance has never been examined. The aim of this study was to test the hypothesis that RV dilation leads to LV diastolic dysfunction after TOF repair. Patients with repaired TOF who underwent cardiac catheterization and cardiac magnetic resonance imaging within 6 months from January 2003 and April 2011 were reviewed to assess the relation of LV end-diastolic pressure (LVEDP) and indexed RV end-diastolic volume (RVEDVi). Thirty-eight patients were included at a median age of 10.1 years (range 0.6 to 54.7). There was a significant linear association between RVEDVi and LVEDP (p = 0.05). RV end-diastolic pressure (p <0.001), right pulmonary artery systolic pressure (p = 0.009), left pulmonary artery systolic pressure (p = 0.02), and total cardiopulmonary support time (p = 0.04) during TOF repair were also significantly associated with LVEDP. Compared to patients with LVEDP <12 mm Hg, those with LVEDP ≥12 mm Hg had significantly higher mean RVEDVi (135.2 ± 47.8 vs 98.6 ± 28 ml/m², p = 0.007) and mean RV end-diastolic pressure (11.7 ± 1.6 vs 8.5 ± 2.8 mm Hg, p = 0.0003). In conclusion, after TOF repair, LVEDP is significantly associated with RVEDVi. Furthermore, mean RVEDVi is significantly higher in patients with LVEDP ≥12 mm Hg. These findings support the theory that RV dilation may impair LV diastolic function and that LV parameters may also be important to consider in determining timing of pulmonary valve replacement.