Hypoplastic left heart syndrome is a condition where the left lower pumping chamber (left ventricle) of the heart does not develop properly so is much smaller than usual. The mitral valve between the left ventricle and the upper left filling chamber (left atrium) is often closed or very small.
An atrioventricular septal defect results in a is a large hole between the upper filling chambers (atria) and the lower pumping chambers (ventricles) of the heart. There is also only one valve between the atria and ventricles instead of two.
The aortic valve is a one-way valve between the left pumping chamber (ventricle) of the heart and the major blood vessel taking blood to the body (aorta). Aortic stenosis (AS) describes a condition where the aortic valve is smaller or tighter than it should be.
Aortic regurgitation occurs when the aortic valve (linking the left ventricle to the aorta) does not close properly when the heart contracts. This means blood leaks back into the left ventricle, which then has to work harder to pump the extra blood away from the heart to the rest of the body. This can lead to the enlargement and thickening of the ventricle wall.