**Core Concept**
The pressure-volume loop is a graphical representation of the relationship between the pressure and volume of the left ventricle during the cardiac cycle. A leftward shift of the pressure-volume loop indicates increased contractility or decreased preload.

**Why the Correct Answer is Right**
In aortic stenosis, the left ventricle is subjected to increased afterload due to the obstruction of blood flow out of the left ventricle. To compensate for this increased resistance, the left ventricle undergoes hypertrophy and increased contractility, resulting in a leftward shift of the pressure-volume loop. This is a classic example of the Frank-Starling mechanism, where increased contractility is a result of increased preload (end-diastolic volume) and afterload.

**Why Each Wrong Option is Incorrect**
**Option A:** Aortic regurgitation would result in a rightward shift of the pressure-volume loop due to increased preload (volume overload).

**Option B:** Mitral regurgitation would also result in a rightward shift of the pressure-volume loop due to increased preload (volume overload).

**Option D:** Congestive cardiac failure would result in a rightward shift of the pressure-volume loop due to decreased contractility and increased preload.

**Clinical Pearl / High-Yield Fact**
The pressure-volume loop is a powerful tool for understanding the pathophysiology of cardiac disease. A leftward shift of the pressure-volume loop indicates increased contractility, while a rightward shift indicates decreased contractility.

**✓ Correct Answer: C. Aortic stenosis**