A 37-year-old man presented with Eisenmenger's reaction. He had progressive cyanosis and signs of right-sided heart failure. In early childhood he was palliated with a Waterston shunt for cyanotic congenital heart disease. Two-dimensional echocardiography provided only a rudimentary view of his heart's anatomy and hemodynamics. Real-time three-dimensional echocardiography (RT3DE) was superior in visualizing both the size and the shape of the large shunt. RT3DE easily identifies and quantifies a key pathogenic factor for pulmonary hypertension with irreversible vascular damage in such patients. If applied early, RT3DE may prove to be a valuable follow-up tool.