The Authors report a case of a serious and symptomatic primary pulmonary hypertension, where the intravenous administration of Diltiazem, at a dosage of 0.3 mg/kg, resulted in an important improvement of haemodynamic parameters. This improvement was confirmed 4 months later on chronic oral therapy with Diltiazem, at a dosage of 180 mg per day. Six months after the beginning of therapy, the patient is totally asymptomatic. Even though further controls are needed, Diltiazem may represent an active drug in the treatment of primary pulmonary hypertension.