Congenital heart block is a rare condition that affects the heart's electrical system, which controls and coordinates its pumping function. In infants affected by this condition, the electrical signal that spreads across the heart and causes it to contract and pump blood, is slowed or completely interrupted. This can interfere with the heart's normal rate and rhythm and may significantly limit the ability of the heart to pump blood to the rest of the body. Congenital heart block generally develops between 18 and 33 weeks of pregnancy. The underlying cause of the condition is poorly understood. However, mothers with lupus or another autoimmune diseases and parents with congenital heart disorders have an increased risk of having a child with a Congenital heart block.