The advanced practice registered nurse (APRN) is assessing an 86 year-old patient. The APRN notes a blowing diastolic murmur (grade Ill out of VI), heard best at the left 2nd through 4th intercostal spaces. What is the most likely cause of the diastolic murmur in this patient?

A. Pulmonary hypertension is incorrect because it may produce a loud pulmonic component of S2 (P2) or possibly a murmur of pulmonic regurgitation, but it is not typically described as a classic blowing diastolic murmur best heard along the left sternal border. B. Right sided heart failure is incorrect because it is a clinical syndrome, not a direct cause of a specific murmur. While it may be associated with murmurs such as tricuspid regurgitation, those are typically holosystolic, not diastolic. C. Left sided heart failure is incorrect because, like right-sided failure, it is a condition rather than a specific valvular lesion. It may be associated with murmurs, but it does not directly produce a blowing diastolic murmur. D. Aortic regurgitation is correct because it classically presents as a blowing, decrescendo diastolic murmur best heard along the left sternal border (2nd to 4th intercostal spaces). This murmur occurs due to backflow of blood from the aorta into the left ventricle during diastole, and is commonly seen in older adults due to degenerative valve changes.