Causes

How the heart normally works

The heart is divided into four chambers, two on the right and two on the left. To pump blood throughout the body, the heart uses its left and right sides for different tasks.

The right side of the heart moves blood to the lungs. In the lungs, blood picks up oxygen then returns it to the heart's left side. The left side of the heart then pumps the blood through the aorta and out to the rest of the body.

Why do heart defects develop?

Doctors know that heart defects present at birth (congenital) arise from errors early in the heart's development, but there's often no clear cause. Genetics and environmental factors might play a role.

How the heart works with an atrial septal defect

A large atrial septal defect can cause extra blood to overfill the lungs and overwork the right side of the heart. If not treated, the right side of the heart eventually enlarges and weakens. The blood pressure in your lungs can also increase, leading to pulmonary hypertension.

There are several types of atrial septal defects, including:

• Secundum. This is the most common type of ASD and occurs in the middle of the wall between the atria (atrial septum).
• Primum. This defect occurs in the lower part of the atrial septum and might occur with other congenital heart problems.
• Sinus venosus. This rare defect usually occurs in the upper part of the atrial septum and is often associated with other congenital heart problems.
• Coronary sinus. In this rare defect, part of the wall between the coronary sinus — which is part of the vein system of the heart — and the left atrium is missing.