A 78 year old male presents to the emergency room with an episode of syncope. He states he had been walking on a treadmill when he became very dizzy and passed out. He has noted exertional chest pressure in the past, but no dizziness or syncope. His temperature is 37.0, blood pressure 120/80, heart rate 90, and respirations 20. Physical examination reveals normal lung sounds, a III/VI late-peaking systolic murmur best heard at the right upper sternal border radiating to the carotid arteries, a II/VI holosystolic murmur at the cardiac apex, an S4 heart sound, an inaudible S2 heart sound, and a weak and delayed carotid impulse. Laboratory studies are normal. Which of the following is the most appropriate initial treatment based on the above?