A case of severe systemic hypertension due to catecholamines discharge after ligation of a large patent ductus arteriosus in an 8 months old child is reported. The blood pressure was corrected by the association of alpha- and betablocker drugs which were withdrawn on the 15th post-operative day without recurrence. Transient increases in blood pressure are quite common after closure of a patent ductus arteriosus with a large shunt. Persistent hypertension greater than 160/110 mmHg is rare. It always regresses but may sometimes cause complications. Hyperactivity of the sympathetic nervous system has already been suggested as a possible cause. Massive discharge of catecholamines and the spectacular effect of the association of alpha- and betablocker therapy, reported here apparently for the first time, provide additional evidence in favour of this hypothesis.