Objective: One of the major causes of mortality in the pediatric intensive care unit (PICU) is heart disease. This study aimed to determine the causes of mortality in children with pre-existing cardiac abnormalities who were admitted into the PICU.Methods: Data were collected through patient profile assessment and outcome and heart diseases affecting prognosis were analyzed. Medical records of children were reviewed retrospectively. The updated Pediatric Index of Mortality 2 (PIM2) scores were used. Exploratory data analysis was performed using descriptive measures. Kolmogorov-Smirnov tests were used to test the normality of data distribution.Results: Out of 566 admissions into PICU, 76 (13.4%) had cardiac abnormalities. Median and range of PICU stay were 5.50 and 417.88 days. The mean PIM2 score on admission was found to be 31.05. The most common admission was due to atrioventricular septal defect (AVSD) (15.7%), cardiomyopathy (13.1%), ventricular septal defect (VSD) (11.8%), tetralogy of Fallot (10.5%) and others (48.9%). There were multiple cardiac anomalies in 3.9% of patients. The most important cause of cardiac mortality in PICU was septic shock (26.0%) followed by cardiogenic shock (20.6%), and cardiac failure (13.7%). The nosocomial infection rate of cardiac patients in PICU was 10.5%.Conclusions: Our study reconfirmed that the PIM2 score is a good indicator of cardiac diseases. Infections, nosocomial infections, pneumonia, and septic shock were the leading causes of mortality in cardiac patients. Better infection control in the PICU may have a significant impact on decreasing mortality rates.