The long-term prospective multi-centre nationwide (French) observational study FRANCISCO will provide new information on perimembranous ventricular septal defect with left ventricular overload but no pulmonary hypertension in children older than 1 year. Outcomes will be compared according to treatment strategy (watchful waiting, surgical closure, or percutaneous closure) and anatomic features of the defect. The results are expected to provide additional guidance about the optimal treatment of this specific population, which is unclear at present.