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: Pediatrics
[{'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: ASD is associated with an enlarged right atrium and 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 Eissenmenger's syndrome develops and a reversal of shunt is seen across the defect. Ref: Essential Pediatrics, 6th Edition By O P Ghai, Pages 400-1.", 'role': 'assistant'}]