Twenty-seven patients, aged 2 months to 3 years, underwent thoracic aorta angiography with balloon inflation during right heart catheterization and cineangiography. The balloon-tipped catheter was manipulated either from the right ventricle to main pulmonary artery and then through patent ductus arteriosus (PDA) or from the right ventricle through ventricular septal defect (VSD) to ascending aorta and to mid-thoracic aorta where the balloon was fully inflated with carbon dioxide. After satisfactory positioning of the inflated balloon, contrast medium was administrated via power injector with a volume of 1.5 ml/kg and a flow rate of 10 ml/sec. Cineangiograms of left lateral projection were obtained. The blood was seen clearly from the thoracic aorta to aortic arch, and also through the PDA to pulmonary vessels. On the late films, left heart chambers were also opacified. Areas of anatomic interest were well visualized in 20 cases of isolated PDA, three of PDA with VSD, two of infantile coarctation of aorta with PDA and VSD, two of tetralogy of Fallot with severe pulmonic stenosis and PDA. This procedure is simple and effective in visualizing the PDA and also, in many occasions, other associated cardiac anomalies. Conventional left heart catheterization and cineangiography could thus be omitted in some cases of congenital heart diseases. There were no untoward complications observed during and after the procedure. This technique is useful especially in critically ill infants.