Bsting,
Your heart murmur is likely due to the problems with your mitral valve and your tricuspid valve, which would not be reasons to keep you from diving. My greatest concern with your heart condition would be the ability of your heart to compensate during exercise. Without knowing more about your physical condition, I cannot comment specifically about your chances for continuing diving, but I can give you some general guidelines.
Your heart condition (hypertrophic cardiomyopathy) is a condition where the heart muscle becomes enlarged, usually as a result of long-standing hypertension, but there some other reasons as well. There are a few different treatment options available, depending on the cause of the cardiomyopathy, but they are basically divided into medically-treated and surgically-treated options. Medicines are usually geared towards reducing the workload of the heart (i.e. reducing blood pressure), while maintaining a good blood supply to the heart tissue itself. Some patients may eventually need surgical treatment in the form of a heart transplant.
How does this effect your chances of continuing diving? Well, the first question I would want answered is: how well can you tolerate exercise? If you can exercise without becoming short of breath (i.e. walk 3 flights of stairs without exhaustion, walk a 12-minute mile, carry out your normal daily activities without becoming winded), there is a good chance that you can continue to dive within reasonable limits. The heart problem itself doesn't increase your risk for developing DCI or air-embolus; the potential for trouble would come if you were not able to get yourself out of a heavy current (or other demanding situation) because of exercise intolerance. There are a host of different medications your doctor may put you on, and many of them are ok to use while diving. Some of them, however, may be of some concern. Without getting into too much detail and specualtion about medication, You should check with your doctor to see if any of them would impair your ability to exercise effectively.
Your doctor should evaluate you for signs and symptoms of heart failure and your ability to perform moderate exercise. He may tell you what your New York Heart Association Heart Failure Classification is (an objective determination of the health of your heart). If your classification is NYHA Class I (very minimal impairment) or zero (i.e. no signs of heart failure), that means you can tolerate moderate exercise well, and you may be able to continue diving. If your doctor gives you a NYHA Class of II or greater, you may putting yourself at considerable risk by continuing to dive. Of course, with medical management, this classification may improve to the point that you can tolerate moderate exercise well, and at that time you should be re-evaluated for your fitness to dive. This classification is one way of determining heart fitness that can be easily extrapolated to diving fitness.
Again, I cannot stress enough the value of open communication between you and your cardiologist. If you tell him/her that diving is important, s/he will be less likely to tell you "no" out of hand. You may even recommend s/he contact DAN if s/he is unsure about the risks of diving with your condition. But the important thing is to be honest with him/her. S/he will know best how to answer your question specifically.
Good luck, and take care,
Dan
