## **Core Concept**
The cardiac cycle consists of several phases, including isovolumic contraction, ventricular ejection, isovolumic relaxation, and ventricular filling. The opening of the aortic valve is a critical event that occurs during ventricular ejection.

## **Why the Correct Answer is Right**
The aortic valve opens when the pressure in the left ventricle exceeds the pressure in the aorta, which typically happens at the start of systole, just after the isovolumic contraction phase. This phase corresponds to the beginning of ventricular ejection. The correct timing for the opening of the aortic valve is at the start of systole, which aligns with the R wave on the electrocardiogram (ECG) or slightly after, marking the onset of ventricular systole.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option suggests the aortic valve opens during late diastole, which is incorrect because the aortic valve opens during systole, not diastole.
- **Option B:** This option implies the aortic valve opens during late systole, which is incorrect because the aortic valve opens at the beginning of systole, not late in systole.
- **Option D:** This option suggests the aortic valve opens during early diastole, which is incorrect because the aortic valve closes at the end of systole and opens during systole.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that the opening and closing of heart valves are directly related to the pressure changes within the heart and great vessels during the cardiac cycle. Specifically, the aortic valve opens when left ventricular pressure exceeds aortic pressure, and it closes when aortic pressure exceeds left ventricular pressure.

## **Correct Answer:** C.