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
A child with large perimembranous VSD has congestive heart failure. What may be the cause of improvement of cardiac failure in the patient – 
Select and explain. 
A. Aortic regurgitation, B. Vascular changes in pulmonary circulation, C. Infective endocarditis, D. Closure of VSD spontaneously
B: Vascular changes in pulmonary circulation
Answer: B: Vascular changes in pulmonary circulation 
Explanation: A patient with large VSD develops CHF because of the large left to right shunt. Large amount of blood at high systolic pressure is entering into the pulmonary circulation and with this continued exposure of the pulmonary vascular bed to high systolic pressure and high flow, pulmonary vascular obstructive disease develops
The pulmonary vascular resistance gradually rises and becomes equal to the systemic resistance. When this happens the shunt becomes bi-directional and the signs of heart failure diminish but the patient becomes cyanotic (Eisenmenenger physiology).