To date, there are no reported cases of the Amplatzer Duct Occluder II: Additional Sizes’ use in percutaneous closure of an aortopulmonary window. We report a case of percutaneous closure of an aortopulmonary window in a 4.5-month-old, 6 kg child. Owing to the patient’s low weight, high risk of damage to the pulmonary valve, as well as the possibility of aortic and pulmonary artery obstruction, classic implants were deemed unsuitable and a decision was made to use the Amplatzer Duct Occluder II: Additional Sizes. The implant performed very well – the soft waist filled the aortopulmonary connection and both retention discs were properly shaped and pressed against vessel walls. Echocardiogram performed 12 hours after the procedure confirmed a correct occluder position. Low-profile retention discs had no impact on pulmonary valve function, despite the defect’s proximity to the valve. No obstruction of the aortic or pulmonary artery lumen was noted. The Amplatzer Duct Occluder II: Additional Size implant is a safe and useful device for percutaneous closure of an aortopulmonary window in a carefully selected group of patients.