A single ventricle is a congenital heart defect where one of the heart's two lower chambers, called ventricles, is underdeveloped or absent. This condition affects the heart's ability to pump blood effectively, leading to inadequate oxygen supply to the body. In individuals with a single ventricle, the heart must work harder to circulate blood, often resulting in complications. Treatment typically involves a series of surgeries to improve blood flow and function, allowing patients to lead more active lives despite the challenges posed by this condition.