This is sometimes known as an endocardial cushion defect because it often involves the endocardial cushion, which is the portion of the heart where the atrial septum meets the ventricular septum and the mitral valve meets the tricuspid valve.

Fixed splitting of the second heart sound (S2) occurs because of equal filling of the left and right atria during all phases of the respiratory cycle.

Features also seen on the ECG include right atrial enlargement and varying degrees of atrioventricular block.

[citation needed] In the ECG above, you can see an example of the rSR' pattern in V1 with a R' greater than S with T wave inversion which is commonly seen in volume overload right ventricular hypertrophy.

[2][3] Hemodynamically significant ASDs (flow ratio 1.5:1) are large enough to be closed surgically.