Is endocardial cushion defect considered a heart disease?

Yes: Unfortunately the names for some defects are confusing. Endocardial cushion defect is an older term. Atrioventricular canal is also an older term for the same entity. The current term for this defect is atrioventricular septal defect and is often abbreviated as avsd.

Yes: Also known as an atrio-ventricular septal defect, or av canal defect, it is a type of congenital heart defect. There is a an ASD and vsd together creating a defect (hole) in the center of the heart. There is also one common av valve , rather than 2 distinct valves (mitral and tricuspid valves). It is commonly but not necessarily associated with down syndrome. Surgical repair is required in infancy.

Yes: These are problems in the middle of the heart affecting the valves and usually requiring surgery to repair.

Words matter: This is a birth defect, where the walls within the heart and sometimes the valves are not formed correctly.It will need some corrective surgery. A heart disease by general definition is a condition where the structures deteriorate over time due to some insult or chronic issue, like a viral heart infection , blood vessel disease from high cholesterol, heart enlargement from hypertension, etc.