BACKGROUND: Published correlations between histological abnormalities and right ventricular (RV) function, as evaluated by speckle tracking echocardiography (STE), are scarce in patients with tetralogy of Fallot (TOF). The purpose of the study is to assess age-associated differences in the effect of RV myocardial remodeling on ventricular function in patients with TOF. METHODS: Operatively resected crista supraventricularis muscle from 30 patients (median age 12months) undergoing intracardiac repair of TOF were studied by light microscopy. The patients were divided into younger (age at surgery ≤12months) and older (age at surgery >12months) subgroups. The RV global longitudinal peak systolic strain (GLS), strain rate (GLSRs) and early diastolic strain rate (GLSRe) were measured by two-dimensional STE before and 6months after repair. RESULTS: The histopathological data revealed hypertrophy of the cardiomyocytes, a thickened endocardium, and increased interstitial and perivascular collagen in RV, which were associated with older age at the time of repair. The RV global systolic and diastolic functions in patients with repaired TOF were increased compared with the preoperative values. The RV cardiomyocyte diameter and collagen volume fraction (CVF) correlated with the preoperative GLS, GLSRs and GLSRe, respectively, in the younger patients (r1=-0.566, P1=0.018; r2=-0.493, P2=0.004; r3=-0.504, P3=0.039). The RV cardiomyocyte diameter and CVF correlated with preoperative GLS, GLSRs and GLSRe, respectively, in the older patients (r1=-737, P1=0.004; r2=-0.588, P2=0.035; r3=-0.812, P3=0.001). The correlation of the RV cardiomyocyte diameter with the postoperative GLS and GLSRe (r1=-665, P1=0.036; r2=-0.787, P2=0.007) and the CVF with the postoperative GLSRs and GLSRe (r1=-762, P1=0.002; r2=-0.713, P2=0.004) were identified only in the older patients. Multivariate analysis indicated that the age at repair was an independent predictor of postoperative GLSRs and GLSRe in all of the patients (ß=-0.449, P=0.041; ß=-0.607, P=0.004). CONCLUSIONS: The effect of RV myocardial remodeling on preoperative RV function was more pronounced in the older patients with TOF than in the younger ones. Preoperative myocardial remodeling affected the postoperative RV function in the older but not in the younger patients. The age at the time of surgical repair was the independent determinant of the postoperative RV myocardial function.