<prompt> In which of the following conditions left atrium is not enlargedVentricular septal defectAtrial septal defectAortopulmonary windowPatent ductus arteriosus  <response>: ASD is associated with an enlarged right atrium right ventricle to accommodate large volume of blood. The left atrium is not enlarged because it decompresses itself by shunting blood to the right atrium at a minor difference in pressure. The left atrium may enlarge once Eisenmengers syndrome develops and a reversal of shunt is seen across the defect.All congenital heart diseases given in option cause left to right shunt.Size of left atrium in left to right shuntsIn left to right shunt, blood enters from left side of heart Lt. atrium, Lt ventricle or aorta to right side of heart Rt atrium, Rt ventricle or pulmonary artery depending on the site of abnormal communication.This blood then flows through pulmonary circulation and again enters the left atrium.The path of blood is then depending on the defect.In all these defects, left atrium recieves larger volume of blood which comes through pulmonary circulation Blood from right side of heart plus some blood from left side of heart because of shunt enter into pulmonary circulation and then into left atrium. So left atrium recieve blood volume larger than normal.But the effect of larger volume on left atrium will be different in ASD and other left to right shunts. 1In ASDLeft atrium recieves extra volume of blood, but fortunate for the left atrium, it also has an extra exit for blood, i.e., septal defect.So, larger volume of blood is decompressed through left atrium.Amount, which is normally exits through AV valve mitral valve into left ventricle.Extra amount, which left atrium recieves, exits through septal defect into right atrium. 2 Other left to right shunts VSD, FDA, Aortopulmonary window.In these defects also, left atrium recieves extra volume of blood, But there is no extra exit.So, left atrium can pump out only normal amount of blood through mitral valve, and extra volume remains in the left atrium Volume over load Left atrial enlargement. 