Q. A healthy 15-year-old female comes to your clinic today with her mother for evaluation of palpitations and shortness of breath. The patient plays basketball on her school team. Recently, she has become easily fatigued, and on a number of occasions complained of a “funny feeling” in her chest. Her symptoms are episodic, self-limiting, and appear to be associated with exercise. She denies any recent fevers or trauma. Her immunizations are up to date, she does not take any medications regularly, and has no history of chronic conditions. On physical examination, she is 157 cm (5 ft 2 in), weighs 54 kg (120 lb), her blood pressure is 120/80 mm Hg, heart rate 60/min, respiratory rate 15/min, and oxygen saturation is 98 percent on room air. Lung auscultation demonstrates clear lung fields bilaterally with no wheezing. Cardiac examination reveals a mid-systolic click along with a high-pitch, holosystolic murmur, best heard at the apex, which is increased with valsalva. Based on the information you have at this point, what is the most likely cause of this patient’s symptoms?