The local YMCA is having a 5K Run, Walk, or Crawl fundraiser. You decide to volunteer at the first aid station to take care of blisters and other minor injuries associated with these events. It is a cool, overcast morning, making it a perfect day for a race, so you do not expect any problems due to hot weather. A call comes in on the two-way radio that a young, adult, male runner just passed out at the 2-K point of the run. You alert the emergency medical technician on duty, and you both head out to see the person. When you get there, the EMT starts questioning the young man, and you record the conversations for the EMT's report. The 25 year old runner commented that he had tightness in his chest followed by chest pain before feeling dizzy and fainting. He also said that he had been short of breath after reaching the 1-K mark. This was the first race he had ever run; however, he said that he takes short walks each night. You learn that he has no history of heart attacks or high blood pressure. He claims that his physical examinations always show low levels of cholesterol and fats in his blood. He also stated that he had a reasonable breakfast and was well-hydrated that morning. The EMT decides to test your knowledge of anatomy and physiology by asking you what may be wrong with the runner. Determine the possible cardiovascular system problems causing the illness.