I have been involved in martial arts since 1968, and also went through an open heart procedure to fix an ascending aortic aneurysm. I think that you should be asking your doctor this question, as the size of your aorta and the rate of change is quite important here. Otherwise, which arts? If you are involved in any throwing arts I would cool it. The impact from falling might be very dangerous. If you are involved in karate or a similar arts it might be ok to practice alone, slowly, and softly. A full blown punch or kick with proper stance, kime, and breath control would, I think, cause a spike in your blood preasure, which is not a good thing with your condition. And for sure I would not kumite until your is fixed. I strong shot to the chest might be fatal.