What cardiac structure is primarily affected in aortic stenosis?

Aortic stenosis specifically affects the aortic valve, which is located between the left ventricle and the aorta. This condition arises when the aortic valve becomes narrowed, restricting blood flow from the heart into the aorta during systole. Consequently, the left ventricle works harder to pump blood through the narrowed opening, which can lead to left ventricular hypertrophy and eventually heart failure if the stenosis is severe and not addressed.

In the context of the other cardiac structures mentioned, the mitral valve, tricuspid valve, and pulmonary valve do not play a direct role in aortic stenosis. The mitral valve is involved in regulating blood flow between the left atrium and left ventricle, the tricuspid valve manages blood flow between the right atrium and right ventricle, and the pulmonary valve controls blood flow from the right ventricle to the pulmonary artery. Each of these valves has distinct functions and implications in various heart conditions but is not affected by aortic stenosis specifically. Thus, the aortic valve is the primary structure impacted in this condition, making it the correct answer.