To elucidate the reversibility of right ventricular (RV) myocardial hypertrophy in tetralogy of Fallot (TF), 30 patients underwent RV endomyocardial biopsies 1 to 25 years (mean 9.7 +/- 6.6) after corrective surgery. Myocardial cell diameter was evaluated by comparing histopathologic data with preoperative patients with TF and normal subjects. As a whole, postoperative cell diameter was smaller than that of age-matched preoperative patients with TF, and larger than that of age-matched normal subjects. In 7 patients without significant residual pulmonary stenosis whose preoperative data were also available, cell diameter significantly decreased after surgery (17.1 +/- 2.1 to 14.0 +/- 2.1 microns, p < 0.01). There was a positive correlation between postoperative cell diameter and age at study (p < 0.01). To negate the influence of age, cell diameter was expressed in terms of a percentage of age-matched normal values (percent cell diameter). There was no significant correlation between percent cell diameter and age at surgery, age at study or the follow-up periods. There were positive correlations between percent cell diameter and the following parameters: RV systolic pressure (p < 0.05), percent normal RV end-diastolic (p < 0.05) and end-systolic (p < 0.01) volumes. These results demonstrate that RV myocardial hypertrophy in TF can regress to some extent after corrective surgery if significant residual pulmonary stenosis is avoided.