Why is it difficult for a baby to get enough oxygen to their tissues when there is a hole between the left and right ventricles?

It is important to remember the function of each of the ventricles. Remeber that the left ventricle pumps oxygenated blood around the body, and the right ventricle pumps deoxygenated blood to the lungs. If there is a hole between these two, blood will flow from the more powerful left ventricle into the right ventricle. This means less of the oxygenated blood in the left ventricle will be pumped through the aorta to reach the tissues.