This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Radiology
[{'content': 'Hilar Dance Sign is seen in - \nSelect and explain. \nA. VSD, B. ASD, C. TOF, D. PDA', 'role': 'user'}, {'content': 'Answer: B \nExplanation: * can be normal in early stages when the ASD is small * Vigorous pulmonary aerial pulsations due to increased blood flow often seen in flouroscopically in pts seen with congenital Lt-Rt shunts especially Atrial Septal Defect. * signs of increased pulmonary flow (pulmonary plethora or shunt vascularity) o enlarged pulmonary vessels o upper zone vascular prominence o vessels visible to the periphery of the film o eventual signs of pulmonary aerial hypeension * chamber enlargement o right atrium o right ventricle o note: left atrium is normal in size unlike VSD or PDA o note: aoic arch is small to normal', 'role': 'assistant'}]