Malnutrition, skeletal muscle wasting, and changes in cardiac muscle mass and function have been described in children infected with the human immunodeficiency virus (HIV). This report analyzes the relation of nutritional status to cardiac muscle mass and function in HIV-infected children. Thirty-six children with symptomatic HIV infection underwent simultaneous anthropometric and echocardiographic evaluations before antiretroviral therapy or supplemental feedings. Nutritional measurements included weight, height, triceps skinfold thickness, and arm muscle circumference. Cardiac measurements included left ventricular mass, contractility, end-diastolic dimension, fractional shortening, blood pressure, and heart rate. In a cross-sectional analysis, children infected with HIV were significantly below age-adjusted standards for height (P = 0.0001), weight (P = 0.0001), triceps skinfold thickness (P = 0.001), and arm muscle circumference (P = 0.04). Left ventricular mass normalized to body surface area was below standard, but contractility was normal. Correlation analyses found an inverse relation between left ventricular mass and weight z score (r = -0.45, P = 0.01), height z score (r = -0.47, P = 0.006), and arm muscle circumference percentile (r = -0.51, P = 0.003). An inverse relation was also found between heart rate and weight z score (r = -0.47, P = 0.007) and arm muscle circumference percentile (r = -0.46, P = 0.007). In malnourished children with HIV infection, a paradoxical relation exists between nutritional status and cardiac muscle mass. The inverse relation between heart rate and nutritional status may suggest altered metabolic rates with possible increased sympathetic tone.