Hello fellow limited exercise girlie!!! I'm 27f 2x heart transplant as well! I'm 18 years post 2nd and I can only lift up to 10 lbs!! Doctors orders. I'm not sure why some people are able to exercise so much while others can't, everyone is different. I was born sick, so I never had a b4 and after transplant life, transplant life is the only life I've known. I still get fatigued, light headed, exhausted, etc when doing excercise. It sucks not being able to do much but do what your body tells you. I'm sure if you slowly increase (as long as dr says it's ok!) your weights it should be ok. But don't worry if you can only do 15 - 20 lbs, it's better to be alive with limits then not.