A 55-year-old man presents with progressive dyspnea on exertion, orthopnea, and paroxysmal nocturnal dyspnea. On physical exam, he has a loud P2, a holosystolic murmur best heard at the apex radiating to the axilla, and an S3 gallop. His blood pressure is 120/70 mmHg, and heart rate is 98 bpm. Which of the following is the most likely diagnosis?

The correct answer to the question "A 55-year-old man presents with progressive dyspnea on exertion, orthopnea, and paroxysmal nocturnal dyspnea. On physical exam, he has a loud P2, a holosystolic murmur best heard at the apex radiating to the axilla, and an S3 gallop. His blood pressure is 120/70 mmHg, and heart rate is 98 bpm. Which of the following is the most likely diagnosis?" is Option B: Mitral regurgitation.

The other options — A) Aortic stenosis, C) Tricuspid stenosis, D) Pulmonic insufficiency — are incorrect for this USMLE Exam Prep question. As explained above: A holosystolic murmur best heard at the apex radiating to the axilla, along with an S3 gallop and symptoms of heart failure, is classic for mitral regurgitation.