The advanced practice registered nurse (APRN) is examining a 70-year-old patient with pulmonary hypertension. On cardiac exam they auscultate a grade II/VI pansystolic (holosystolic) murmur of medium pitch at left lower sternal border which radiates to the right of the sternum (xiphoid area). The APRN asks the patient to inspire and notes an increase in the intensity of the murmur. Which is the most likely physiological cause of the murmur?

A. Tricuspid valve regurgitation is correct because a holosystolic murmur at the left lower sternal border that increases with inspiration is classic for tricuspid regurgitation. Inspiration increases venous return to the right heart, augmenting right ventricular stroke volume and thus intensity of right-sided murmurs. The murmur radiates toward the xiphoid area or right sternal border, consistent with the anatomical location of the tricuspid valve. B. Pulmonic valve regurgitation is incorrect because it produces a diastolic murmur, usually early diastolic, best heard at the upper left sternal border and often increases with expiration, not inspiration. It does not present as a holosystolic murmur at the left lower sternal border. C. Mitral valve regurgitation is incorrect because it causes a holosystolic murmur at the apex of the heart, radiating to the axilla, and its intensity does not increase with inspiration. Mitral regurgitation is a left-sided murmur, so it is not affected by inspiration in the same way as right-sided murmurs. D. Aortic valve regurgitation is incorrect because it produces an early diastolic decrescendo murmur best heard at the right upper sternal border. It is a left-sided diastolic murmur, not holosystolic, and does not increase with inspiration.