If it fits your world paradigm, I would suggest prayer. Mindful prayer and rote prayer are very helpful in coping with fear and anxiety. For myself, I say the rosary in my head using my fingers to count. Prayer helps you reach a place of peace, whether in God, inside you or with the universe.
From reading your posts, since you are asymptomatic, it seems you have trouble believing the surgery is needed now. I had the same problem. What turned my head was reading a paper on deaths from BAV (our valve problem.) The age ranged from 16 to 80 with the median at 54 (my age at surgery.) This pushed me over the edge and into acceptance. I realized that I was "average" for a BAV, but also that each one of the ~100deaths were preventable if caught and treated in time.
I then had an episode of dizziness and acceptance went to happiness that I had time to have christmas and spend some time with my family before I started the adventure. I wanted the surgery to live. While waiting, when I started dwelling on the fear, I would go do something with my dog, kid or spouse. Try to find distractions that are supportive.