Left ventricular (LV) mass and function in 11 patients (group 1) with coarctation of the aorta repaired at a mean age of 35 days were compared with that of 14 patients (group 11) who under went repair at a mean age of 8 years. Each group was compared to age- and sex-matched normal control subjects. All patients were normotensive and had resting arm4eg peak systolic blood pressure gradients c20 mm Hg. Quantitative M-mode echocardiography was used to determine LV mass index and systolic performance. Magnetic resonance imaging was performed to assess residual narrowing of the descending aorta. LV mass index was increased in both groups when compared with control subjects (group I p = 0.01; group 11 p = 0.007). Whereas systolic performance in group I was similar to its control group, group II patients had enhanced LV systolic performance as measured by shortening fraction (p = 0.007). Multiple regression analysis of combined group I and 11 patients demonstrated a significant positive correlation of residual aortic narrowing with LV mass index (p = 0.01). Thus, LV mass remains increased in normotensive patients without major blood pressure gradients after repair of coarctation of the aorta in infancy or childhood. Small degrees of residual aortic narrowing were associated with increased postoperative LV mass regardless of the age at repair.