DILV is one of several heart defects known as single (or common) ventricle defects. People with this condition generally have a large left ventricle (the pumping chamber of the heart that supplies the body with blood), and a small right ventricle (the pumping chamber that supplies the lungs with blood).
In the normal heart, the right and left lower chambers (ventricles) receive blood from the right and left upper chambers (atria). Oxygen-poor blood returning from the body flows to the right atrium and right ventricle. The right ventricle then pumps blood to the pulmonary artery, which carries blood to the lungs to pick up oxygen.
The blood, now oxygen rich, returns to the left atrium and left ventricle. The aorta then carries oxygen-rich blood to the rest of the body from the left ventricle.
However, in those with DILV, only the left lower heart chamber is developed, and both upper chambers carry blood into this ventricle. This means that oxygen-rich blood mixes with oxygen-poor blood. The mixture is then pumped into both the body and the lungs.
DILV can occur with transposition of the great vessels (in which the aorta arises from the small right ventricle and the pulmonary artery arises from the left ventricle), or it can occur with the arteries arising from their "normal" ventricles. Blood flows from the left to right ventricle through a ventricular septal defect (VSD) -- a hole between the chambers.
Double inlet left ventricle occurs in about 5 - 10 of 100,000 live births. The problem most likely occurs early in the pregnancy, when the baby's heart develops. However, the exact cause of DILV is unknown.
Patients with DILV often also have other heart problems, such as: