This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Medicine
[{'content': 'In which of the following conditions left atrium is not enlarged: \nSelect and explain. \nA. Ventricular septal defect, B. Atrial septal defect, C. Aoopulmonary window, D. Patent ductus aeriosus', 'role': 'user'}, {'content': "Answer: B \nExplanation: Answer is B (ASD) ASD is associated with an enlarged right atrium & right ventricle to accommodate large volume of bloilL 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 Eisen menger's syndrome develops and a reversal of shunt is seen across the defect.", 'role': 'assistant'}]