A 38-year-old man presents to the clinic with a 6-month history of progressive fatigue and shortness of breath with exertion. He works as a landscaper and has found it increasingly difficult to keep up with the physical demands of his job. He also reports occasional palpitations, especially when lying on his left side. He recalls being told he had a “heart murmur” as a child but never had it investigated. He has no other medical problems and takes no medications. His family history is notable for his father's sudden death from a presumed “heart attack” at the age of 50. He drinks alcohol socially and denies any history of smoking or illicit drug use.