ObjectiveTransposition of great arteries is a common cyanotic heart defect. Balloon atrial septostomy aims to improve circulatory mixing and oxygenation. Previous studies have combined infants with intact ventricular septum and those with ventricular septal defect. Additionally, the septostomy was performed much later after birth. The objectives were to ascertain any correlation between the atrial septal defect size and oxygenation, before and after septostomy, as well the change in parameters pre-post procedure.MethodsWe performed an audit of the last 10 years of clinical and echocardiographic data (2010–2020) for infants with transposition of great arteries with intact ventricular septum. A pediatric cardiologist, masked to clinical data, reviewed the images.ResultsOur study of 25 infants with transposition of great arteries with intact ventricular septum noted that the procedure was performed at a median interquartile range (IQR) of 3 (2, 4) hours after birth. Prostaglandin was administered to the majority of infants 20/25 (80%). While significant increases in partial pressure of oxygen (24±5 vs 40±6 mmHg, p<0.001) and preductal oxygen saturations (67%±18% vs 81%±11%, p=0.003) were noted, and while the atrial septal defect increased in size from 1.8±0.6 vs 4.8±0.7 mm (p<0.001), no correlation was noted between atrial septal defect size and oxygen saturations.ConclusionsIn our study of infants with transposition of great arteries and intact ventricular septum managed with balloon atrial septostomy, no correlation was noted between the atrial septal defect size and oxygen saturations. Pulmonary vascular resistance and pulmonary blood flow may be important physiological variables determining oxygenation.