Cardiovascularcommon
A 76-year-old man is brought to the emergency department after losing consciousness while pushing his lawnmower up a slope. His wife reports he went pale and collapsed for less than a minute, recovering quickly without confusion or incontinence. For six months he has been increasingly short of breath walking up hills, with occasional exertional chest tightness. His blood pressure is 118/92 mmHg, and the carotid pulse is of small volume and rises slowly. There is a harsh systolic murmur loudest at the right second intercostal space radiating to both carotid arteries, and the second heart sound is soft. Which one of the following is the most likely diagnosis?