An 8 year old girl with primary pulmonary hypertension and signs of heart failure was given 17.5 mg of verapamil injected into the pulmonary artery over 25 minutes to test for the reversibility of pulmonary arteriolar obstruction. Pulmonary artery pressure fell from 70/50 to 35/25 mm Hg. Treatment with 40 mg verapamil by mouth four times daily was started, and she was discharged. She gradually became asymptomatic and resumed the activities of a normal child of school age. On recatheterisation seven months later her pulmonary artery pressure was 30/10 mm Hg. She was still doing well 12 months after the start of treatment.