Which of the following does not form left border of heart?
**Core Concept**
The cardiac silhouette is formed by the pericardium, cardiac chambers, and major vessels. The left border of the heart is a critical landmark for diagnosing cardiac abnormalities, and it is formed by several structures. In particular, the left ventricle, left atrium, and aortic arch contribute to the left border of the heart.
**Why the Correct Answer is Right**
The left border of the heart is primarily formed by the left ventricle, which is the largest portion. The left atrium also contributes to the left border, especially in individuals with a larger left atrium. The aortic arch, which arises from the left ventricle, also forms part of the left border. The pulmonary artery, on the other hand, arises from the right ventricle and contributes to the right border of the heart.
**Why Each Wrong Option is Incorrect**
**Option A:** The left ventricle is a major contributor to the left border of the heart, so this option is incorrect.
**Option B:** The left atrium also contributes to the left border of the heart, especially in individuals with a larger left atrium, making this option incorrect.
**Option C:** The aortic arch arises from the left ventricle and contributes to the left border of the heart, so this option is incorrect.
**Clinical Pearl / High-Yield Fact**
In chest radiography, the left border of the heart is often used as a landmark to diagnose cardiac abnormalities. A widened left border may indicate left ventricular enlargement, while a normal left border suggests a normal left ventricle.
**Correct Answer: D. Pulmonary artery. The pulmonary artery arises from the right ventricle and contributes to the right border of the heart.**