Can I maintain a high level of physical fitness,, weight training, cardio, martial arts and not cause more heart damage if I do have cardiomyopathy, I train like a proffessional athlete but since my diagnosis I'm a little afraid
Exercise to the full extent your doctor recommends. Regular exercise strengthens the heart and lowers blood pressure.
I think everyone's level varies depending on what they are used to doing. I wouldn't go any further than you feel comfortable with. I am sure you will know what your tolerance will be. Don't allow fear to rule you in any way, learn to know and recognize your limits, and stay within those.
Is your cardiomyopathy (enlarged heart) due to an "athletes" heart?. That condition may be to some degree identified with a slow heart rate at rest (<60 bpm). That condition is not pathological and almost always will not be a problem....the heart will return to normal size after a short period of no exercise. No restrictions for cardiovascular reasons.
If the cardiomyopathy is a pathological condition, the underlying cause should be determined and your doctor would be the best source for your exercise tolerance and limitations. Weight training is not advised for some heart condtions, etc. As Ally states some exercise is beneficial and for an aerobic exercise (220 minus your age) is the target heart rate to sustain for a half hour or so for a good heart workout at least 3 times a week.