A 15-year-old athlete is in your office for his annual physical examination before the start of football season. He has no complaints, has suffered no injuries, and appears to be physically fit. On his heart examination, you note a heart rate of 100 beats per minute, and a diffuse point of maximal impulse (PMI) with a prominent ventricular lift. He has a normal S1 and S2, with an S4 gallop. He has no murmur sitting, but when he stands you clearly hear a systolic ejection murmur along the lower left sternal edge and the apex. For which of the following conditions is this examination most consistent?
a) Hypertrophic cardiomyopathy
b) Aortic stenosis
c) Mitral valve prolapse
d) Atrial septal defect