Background: Heart disease is a debilitating condition contributing to high morbidity and mortality rates as well as high disease burden among children. The aim of this study was to establish the characteristics of children with heart disease aged 0-12 years in Kenyatta National Hospital (KNH). Methods: A descriptive cross-sectional study was conducted among 92 children with heart disease admitted in paediatric wards of KNH, Kenya. Results: Of the 92 children (54.3%) were infants and (52.2%) were males. Mean age was 2.4(+3.4) years. The mean age at diagnosis for congenital heart disease and acquired heart disease was 23 months and 6.09 years respectively. Most (79.3%) children had congenital heart defects; Ventricular septal defect (22.8%) being the most prevalent. Rheumatic heart disease and dilated cardiomyopathies were the most common (5.4%) acquired conditions. Forty nine (53.3%) children had heart failure.Characteristics with statistical significance were; slow weight gain [P=0.008], cyanosis [P=0.032], use of accessory muscles of respiration [P=0.007] and heart murmur [P=0.001] for children with congenital heart defects while weight loss [p≤ 0.001], dyspnoea [p≤ 0.001], abnormal pulsations [P=0.001], cardiac failure [p≤ 0.001], weakness/fatigue [p≤ 0.001] and polyarthritis [p≤ 0.001] were significant for children with acquired heart disease Conclusion: Congenital heart defects are the most common heart conditions in KNH commonly affecting infants and male children. There was a likely delayed diagnosis of congenital heart disease as about half the children presented already in heart failure on admission.