Hi, 
I have Thalassemia Intermediate, with an average hemoglobin level of about 10, no transfusions so far, and I have been weightlifting for 3 years.
I really enjoy pushing my body to the limit through weightlifting in order to enlarge my muscles.
Unfortunately, over the course of the 3 years, along with my muscles growing my heart has grown too!
Every time I visit the cardiologist he insists that I stop pushing my body with the intensity I have done so far. He suggests scaling down the weight  I lift and try lifting lower weights with higher repetitions. 
Unfortunately, this has not yielded the results I desire. 
I am looking for any sort of advise on how to balance heavy exercise and muscle growth with a healthy heart.
I definitely do not want weightlifting to cause any short-term or long-term heart issues as my cardiologist suggests (if my heart grows to big I  will have to transfuse, or something along those lines)will  happen if I continue at this rate. 
Any advise would be greatly appreciated.
Thanks!