IMPORTANCE Prior to contemporary antiretroviral therapies (ARTs), children infected with human immunodeficiency virus (HIV) were more likely to have heart failure. This study suggests that highly active ART (HAART) does not appear to impair heart function. OBJECTIVE To determine the cardiac effects of prolonged exposure to HAART on HIV-infected children. DESIGN In the National Institutes of Health-funded Pediatric HIV/AIDS Cohort Study's Adolescent Master Protocol (AMP), we used linear regression models to compare echocardiographic measures. SETTING A total of 14 US pediatric HIV clinics. PARTICIPANTS Perinatally HIV-infected children receiving HAART (n = 325), HIV-exposed but uninfected children (n = 189), and HIV-infected (mostly HAART-unexposed) historical pediatric controls from the National Institutes of Health-funded Pulmonary and Cardiovascular Complications of Vertically Transmitted HIV Infection (P2C2-HIV) Study (n = 70). EXPOSURE Long-term HAART. MAIN OUTCOMES AND MEASURES Echocardiographic measures of left ventricular (LV) function and structure. RESULTS The 325 AMP HIV-infected children had lower viral loads, higher CD4 counts, and longer durations of ART than did the 70 HIV-infected children from the P2C2-HIV Study (all P < .001). The z scores for LV fractional shortening (a measure of cardiac function) were significantly lower among HIV-infected children from the P2C2-HIV Study than among the AMP HIV-infected group or the 189 AMP HIV-exposed but uninfected controls (P < .05). For HIV-infected children, a lower nadir CD4 percentage and a higher current viral load were associated with significantly lower cardiac function (LV contractility and LV fractional shortening z scores; all P = .001) and an increased LV end-systolic dimension z score (all P < .03). In an interaction analysis by HIV-infected cohort, the HIV-infected children from the P2C2-HIV Study with a longer ART exposure or a lower nadir CD4 percentage had lower mean LV fractional shortening z scores, whereas the mean z scores were relatively constant among AMP HIV-infected children (P < .05 for all interactions). CONCLUSIONS AND RELEVANCE Long-term HAART appears to be cardioprotective for HIV-infected children and adolescents.