**Question:** During cardiac examination of a newborn infant, a murmur is detected and the diagnosis of patent ductus arteriosus is made. Which of the following best describes the direction of blood flow through the patent ductus arteriosus in this infant?

A. Pulmonary artery to aorta
B. Aorta to pulmonary artery
C. Aorta to pulmonary artery
D. Aorta to systemic artery

**Correct Answer:** C. Aorta to pulmonary artery

**Core Concept:**
A patent ductus arteriosus (PDA) is a congenital heart defect where the ductus arteriosus, a small vessel that normally closes shortly after birth, remains open. The ductus arteriosus connects the aorta (the main artery that carries oxygenated blood to the body) to the pulmonary artery (the main artery that carries deoxygenated blood to the lungs for oxygenation). In a newborn with a PDA, blood flows from the aorta to the pulmonary artery, bypassing the lungs where blood should undergo oxygenation.

**Why the Correct Answer is Right:**
In this case, the correct answer is C. Aorta to pulmonary artery, because the patent ductus arteriosus connects the aorta to the pulmonary artery. When the ductus arteriosus remains open, oxygenated blood (from the aorta) flows through the ductus arteriosus into the pulmonary artery, bypassing the lungs and causing deoxygenated blood to flow into the pulmonary circulation.

**Why Each Wrong Option is Incorrect:**
A. Pulmonary artery to aorta: This option is incorrect because the ductus arteriosus connects the aorta to the pulmonary artery, not the pulmonary artery to the aorta.
B. Aorta to pulmonary artery: This option is similar to the correct answer but is wrong because it is describing the wrong direction of blood flow through the ductus arteriosus.
D. Aorta to systemic artery: This option is incorrect because the ductus arteriosus is connecting the aorta to the pulmonary artery, not to a systemic artery. Systemic arteries carry deoxygenated blood to the body, while the pulmonary artery carries deoxygenated blood from the heart to the lungs for oxygenation.

**Clinical Pearl:**
In cases of patent ductus arteriosus, newborns may present with cyanosis (blue discoloration of the skin due to insufficient oxygenation), respiratory distress, and poor feeding. Early diagnosis and management are crucial to prevent complications like congestive heart failure and lung complications. Treatment options include medications (like indomethacin or ibuprofen) to close the ductus arteriosus or surgical intervention in severe cases.