There have been few reports describing the use of carvedilol in children or patients with congenital heart disease. Therefore, its optimal regimen, efficacy, and safety in these patients have not been adequately investigated. Subjects were 27 patients with two functioning ventricles, for whom carvedilol was initiated (from December 2001 to December 2005) to treat heart failure. All patients had failed to respond to conventional cardiac medication. They consisted of 12 males and 15 females, aged 23 days to 47 years (median age: 2 years). Heart failure due to ischemia (myocardial infarction, intraoperative ischemic event) or due to myocardial disease (cardiomyopathy, myocarditis), and heart failure with atrial or ventricular tachyarrhythmia represented 70% of all cases. Carvedilol was initiated at a dose of 0.02-0.05 mg/kg/day, which was increased by 0.05-0.1 mg/kg/day after 2 days, 0.1 mg/kg/day after 5 days, and 0.05-0.1 mg/kg/day every month thereafter with a target dose of 0.8 mg/kg/day. This study retrospectively assessed the efficacy and adverse reactions based on changes of symptoms, cardiothoracic ratio (CTR), left ventricular ejection fraction (LVEF), and human atrial natriuretic peptide (hANP)/b-type natriuretic peptide (BNP) blood levels. The mean follow-up period was 10.2 months (range: 1-46 months). Twenty-six (96.3%) patients showed improvement in symptoms and were discharged from the hospital. However, the remaining one patient failed to respond and died. Significant cardiovascular adverse reaction was seen in none of the patients. The mean CTR decreased from 61.8% +/- 5.3% before treatment to 57.6% +/- 7.4% after treatment (P < 0.05, n = 25), and the mean LVEF improved from 41.4% +/- 23.1% to 61.1% +/- 10.1% (P < 0.05, n = 10), respectively. Mean hANP and BNP levels showed a decrease from 239.1 pg/ml to 118.3 pg/ml and a significant decrease from 437.9 pg/ml to 120.5 pg/ml, respectively (P < 0.05, n = 10). Improvements in these data were also demonstrated when analyzed individually among the pediatric group (aged younger than 18) and the congenital heart disease group. Initiation of carvedilol at a lower dose with more gradual dose escalation, compared with previously reported regimens, might have efficacy with low incidence of adverse effects in pediatric patients and patients with congenital heart disease. Carvedilol may be effective in treating heart failure in children due to ischemia, myocardial disease, and complicated by tachyarrhythmia.