During cardiac development, the primitive interventricular foramen (IVF) is closed primarily by fusion of which three structures?

• A Septum primum, septum secundum, and endocardial cushions
• B Aorticopulmonary septum, sinus venosus septum, and conus septum
• C Bulbus cordis, primitive atrium, and sinus venosus
• D Muscular interventricular septum, endocardial cushions, and conotruncal septum ✓

Explanation

The interventricular foramen is closed by growth from three sources: (1) the muscular interventricular septum growing superiorly from the apex; (2) the endocardial cushions (atrioventricular) contributing membranous septum tissue; and (3) the conotruncal (bulboventricular) septum spiraling down from above. Failure of this three-way fusion causes membranous VSD, the most common type of VSD. Septum primum and secundum close the foramen ovale in the atria. The aorticopulmonary septum spirals between the aorta and pulmonary trunk within the truncus arteriosus.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

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