There are two types of ASD, ostium secundum and ostium primum. The former is the most common, and is sometimes due to fenestrated ASD (i.e. multiple small defects). Ostium primum is less common, but is often seen in patients with Down’s syndrome. It is also associated with mitral regurgitation.

Small defects, such as those associated with ostium secundum have also been described as machinery murmurs. In ostium primum defects, the pulse may be collapsing and there may be a possible mid-diastolic tricuspid flow murmur.

ECG changes with ASD include an rSr pattern in the right precordial leads as well as right axis deviation (with ostium secundum defects) whereas left axis deviation is associated with ostium primum defects.