**Core Concept**
Aortic valve closure corresponds to the beginning of the isovolumetric contraction phase of the cardiac cycle. This is a crucial event in cardiac physiology, marking the transition from diastole to systole.

**Why the Correct Answer is Right**
During ventricular contraction, the ventricular pressure increases rapidly and eventually exceeds the aortic pressure. At this point, the aortic valve closes to prevent backflow of blood into the ventricles. This closure marks the beginning of the isovolumetric contraction phase, where the ventricular pressure continues to rise while the volume remains constant. The aortic valve closure is closely related to the opening of the mitral valve, which allows blood to flow from the left atrium into the left ventricle.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because aortic valve closure does not correspond to the beginning of the rapid ejection phase, which occurs later in systole.
**Option B:** This option is incorrect because aortic valve closure does not correspond to the beginning of the isovolumetric relaxation phase, which occurs in diastole.
**Option C:** This option is incorrect because aortic valve closure does not correspond to the beginning of the early diastolic filling phase, which occurs after the isovolumetric relaxation phase.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the closure of the aortic valve marks the transition from diastole to systole, and is an important event in the cardiac cycle.

**Correct Answer: C.**