**Core Concept:** Cardiac dominance refers to the dominant coronary artery that supplies blood to the heart muscle. The primary coronary arteries are the left coronary artery (LCA) and the right coronary artery (RCA). In humans, either the LCA or RCA is the dominant coronary artery, ensuring adequate blood supply to the heart.

**Why the Correct Answer is Right:** In humans, cardiac dominance is determined by the dominant branch of the left coronary artery, which is the LCA. The LCA has two major branches: the left anterior descending artery (LAD) and the left circumflex artery (LCx). The LAD is the dominant coronary artery in approximately 90% of cases, as it provides the majority of blood flow to the heart muscle. In cases of LAD dominance, the heart is considered "left-dominant" or "left-sided dominance."

**Why Each Wrong Option is Incorrect:**

A. Right coronary artery (RCA) dominance is incorrect because the RCA is the dominant coronary artery in only about 10% of cases. The RCA supplies blood to the posterior wall of the heart, and dominance of this artery would lead to insufficient blood supply to the left ventricle and the anterior wall of the heart.

B. Dominance of the left circumflex artery (LCx) is incorrect because the LCx is a branch of the LCA, not the RCA. In left-sided dominance, the LCA is the dominant coronary artery, ensuring sufficient blood supply to the ventricles and the anterior wall of the heart.

C. Dominance of both RCA and LCx is incorrect as it would result in insufficient blood supply to the ventricles and the anterior wall of the heart. Dominance of a single coronary artery (either LCA or RCA) ensures adequate blood flow to the heart muscle.

D. Dominance of the right coronary artery (RCA) is incorrect as the RCA is a branch of the LCA and is less likely to be dominant. Dominance of the LCA ensures sufficient blood supply to the ventricles and the anterior wall of the heart.

**Clinical Pearl:** Understanding cardiac dominance is essential for diagnosing and managing myocardial infarction (heart attack) and coronary artery disease. A left-sided dominance allows for better blood supply to the heart, while a right-sided dominance may indicate inadequate blood flow, leading to ischemic complications.