170) Answer

C. Aortic stenosis

Rationale

•Aortic stenosis is the narrowing of the aortic valve. This causes reduced cardiac output and increased left ventricle pressure.

•With exertion, the heart cannot increase cardiac output because of a narrow aortic valve. This can cause syncope due to insufficient perfusion to the brain. Syncope is a hallmark sign of aortic stenosis.

•Aortic regurgitation and mitral stenosis do not cause syncope.