We have read the letter regarding the use of duct occluders for the closure of perimembranous ventricular septal defects by Yilmazer et al,Reference Murat, Timur and Baris ¹ which cites our publication,Reference Mahimarangaiah, Subramanian and Kikkeri Hemannasetty ² in an earlier issue of Cardiology in the Young. Although Amplatzer Duct Occluder II devices have been used more often in locations other than the ductus, the same cannot be said of first-generation duct occluders. We are now aware of several centres in the west and south-east Asia, where conventional duct occluders have been successfully used for closure of perimembranous ventricular septal defects, although published data are scanty. This might partly be because of reluctance to publish an off-label use of an otherwise popular device. The authors’ observation regarding development of transient left bundle branch block with an Amplatzer Duct Occluder II device was, nevertheless, discomfortingly surprising. The development of left bundle branch block, following device or surgical closure of perimembranous ventricular septal defects, is by and large uncommon, as the left bundle fans out into anterior and posterior fascicles soon after its origin. The atrioventricular node, rather than the bundle branches, is located in close relation to a membranous ventricular septal defect. In contrast, the bundle branches course anterior to a defect in the muscular septum. The posterior fascicle occupies the full thickness of the septum; involvement of both fascicles to cause a complete left bundle branch block would be very unlikely by a device in the perimembranous region, unless the patient had a variant anatomy of the His bundle or the defect was more membrano-muscular, rather than truly perimembranous. The right bundle is anatomically more vulnerable, and development of right bundle branch block following closure of perimembranous defects has been more often reported in the literature. Their observation underscores the importance of anticipating and watching out for conduction disturbances several years after device or surgical closure of defects in this region.