An 18 year old male with no significant past medical history passes out while running. He states that he was feeling a little dizzy prior to the event, but no chest pains or palpitations. His blood pressure is 115/85, heart rate 80, respirations 12, and he is afebrile. His physical examination reveals normal lung sounds, a II/VI mid-systolic crescendo-decrescendo murmur is heard at the right upper sternal border which increases in intensity with Valsalva, an S4 heart sound is also present. Laboratory studies are normal. What is the most appropriate treatment at this time?
A. Start a diuretic
B. Implantation of a pacemaker
C. Implantation of a defibrillator
E. Atrial septal defect