Is an endocardial cushion defect considered heart disease?

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.