i started climbing 2 years before my avr and i was able to start climbing again 6 weeks after. literally the day after i was given the go ahead to resume physical activity - after my sternum was deemed "healed" - i resumed my climbing gym membership. admittedly, i prob started climbing hard a bit soon, but i was going nuts just sitting at home. i found that i was not nearly as strong (obviously, after loosing 18 pounds), but my finger strength remained and i didnt have any real chest pain, just a bit of discomfort. nothing that didnt stop me from climbing everyday for the next week. i was actually climbing reasonably well. before surgery, i was projecting 5.12b, leading 5.10 and bouldering v6. i havent been climbing as much as i was before surgery, but i can redpoint 5.11a and boulder v5. i havent lead outdoors yet because of the weather, so ....
one thing: i choose a donor valve because dealing with coumadin managment imho, was something i didnt want to be an issue as a 22 year old (i have a hard enough time taking 3 pills once daily!)with the rest of his hopefully long life to live, but i also race road and mtn bikes (road rash and bleeding would def be an issue since i crash at least once a season). also, im a thai boxer who trains/fight, so bruising/cuts are a very big issue there. a mech valve just didnt work for me, but the most physical thing you do is climb, i dont think it would be prohibitive.
best wishes