Cardiac mass and function were evaluated in 10 children with classical GH deficiency. Echocardiograms were performed at baseline, 3, 6, and 12 months after initiation of recombinant human (rh) GH therapy (0.3 mg/kg.wk). Before treatment, left ventricular (LV) mass indexed to body surface area (BSA) was low or low normal (<50 g/m(2)) in five children compared with reference control data. Height SD score (-3.2 +/- 0.9 vs. -1.8 +/- 1.3 yr; P < 0.01), growth velocity SD score (-2.7 +/- 1.6 vs. 5.8 +/- 3.1; P < 0.01), LV mass (36 +/- 9 vs. 60 +/- 30 g; P < 0.02), LV mass/BSA (51 +/- 12 vs. 72 +/- 11 g/m(2); P < 0.01), LV mass/height (36 +/- 9 vs. 54 +/- 15 g/m; P < 0.02), and LV mass/m(2.7) (36 +/- 12 vs. 45 +/- 8; P < 0.05) increased significantly with rhGH therapy. Pretreatment LV mass/BSA correlated inversely with fold increase in LV mass/BSA over the year (r = -0.83; P < 0.01). Load-dependent indices of diastolic performance were normal at baseline and did not change with rhGH therapy. Percentage increase of mean velocity of circumferential shortening, an index of systolic function, correlated with fold increase in LV mass/BSA (r = 0.88; P < 0.02) over the year of rhGH administration. LV mass can be lower than predicted for body size in some children with severe GH deficiency but is responsive to rhGH replacement. LV mass/BSA increases into the normal range during the first year of rhGH therapy. The rate of increase of LV mass is greater than the increase in BSA during rhGH treatment, suggesting that GH could also be a trophic factor for the heart.