A small, thin, 4-year-old boy presents with an audible continuous murmur that is heard near the left proximal clavicle and is present throughout the cardiac cycle. The murmur is louder in systole than diastole. Which of the following conditions is most likely the cause of this murmur?

A. Atrial septal defect

B. Mitral stenosis

C. Patent ductus arteriosus

D. Right ventricular hypertrophy

E. Ventricular septal defect

Answer: C. Patent ductus arteriosis

Explanation:

Patent ductus arteriosis is a physiological condition in which the ductus arteriosus does not close after birth. This results in the flow of the oxygenated blood from the left heart to flow back to the lungs by passing through the aorta.

The blood in the aorta is at high pressure. This results in continuous murmur due to the generation of the constant pressure gradient in the diastole and the systole, that forces the blood from the aorta to the pulmonary artery. The murmur sound is louder in the systole than in diastole.

Based upon the above explanation, Patent ductus arteriosis is the condition that is responsible for the murmur.