Background: Congenital heart diseases (CHD) are common congenital anomalies that account for a significant proportion of mortality and morbidity in children. Presentation of CHD varies from asymptomatic discovered accidentally to severe and debilitating complications and death. Early diagnosis and treatment have great effects on prognosis. Inadequate knowledge on the patterns of CHD, associated risk factors and its treatment outcomes impede the development of appropriate interventions. Objective: This study evaluated the patterns and risk factors of congenital heart disease and treatment outcomes during acute phase hospitalization among children aged under 5 years at Kenyatta National Hospital (KNH). Methods: This was a retrospective case-control study, involving children aged below 5 years admitted to KNH’s Pediatric Unit between 1st January, 2017 and 31st December, 2021 who had CHD. A total of 2,450 medical records of pediatric patients were reviewed. A similar number of health records (matched for age) without CHD was used as a control group. The researcher used census method whereby all pediatric patients’ health records with documented CHD case and their matched controls, under the specified period, were reviewed. The data was extracted from the pediatric patients’ medical records, kept at the hospital’s Records department, using a data abstraction form. The outcome of interest included mortality and recovery rates. The study data was analyzed descriptively using SPSS version 25 and presented in form of frequencies and percentages. In addition, chi-square test statistic and odds ratios were utilized to analyze the study variables’ association at 5% significance level. Findings of the study were summarized in tables and figures. Results: Over the period 2017 to 2021, ventricular septal defect cases rose from 74 to 116 (a 56.8% rise); atrial septal defect cases rose from 45 to 74 (a 64.4% rise); patent ductus arteriosus cases rose from 61 to 85 (a 39.3% rise) while pulmonary valve stenosis cases rose from 31 to 47 (a 51.6% rise). Ventricular septal defect (27.4%), was the most prevalent CHD. Risk factors of CHD included multiple pregnancy (Chi square p = 0.002); lack of access to prenatal care during pregnancy (Chi square p = 0.000); maternal diabetes mellitus (Chi square p = 0.000); maternal medications use during pregnancy (Chi square p = 0.019) and prematurity (Chi square p = 0.000). The risk factors of CHD established to have a statistically significant association with poor treatment outcomes among the children included; infants’ down syndrome (Chi square p = .000; OR = 4.52) and prematurity (Chi square p = .007; OR = 2.21). Recovery rate in the CHD group was 87.3% while the mortality was 12.7%. Conclusion: There was an increasing trend of prevalence of the CHD defects in children in KNH over the five-year period. Children with cyanotic CHD, on average, had 3 times higher odds of dying from CHD compared to those with acyanotic CHD. Infants’ down syndrome and prematurity were the risk factors related to poor treatment outcomes of CHD among children admitted at KNH. Recommendations: The increasing trend of CHD needs further evaluation. Staff sensitization on diagnosis of CHD, since the most common CHDs are acyanotic which are not easy to identify. Infants’ down syndrome and prematurity require more attention and specialized care.

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