What will the doctor recommend for the cure, if the heart muscle is very weak almost totally damaged, but the person still
feel strong and can perform daily routine, like playing tennis, walking upstair. etc.
As long as there aren't any major limiting symptoms I would continue with medical therapy. There is no cure for heart failure, but we can make people feel relatively well. Some patients may benefit from device therapy if symptoms develop. The most aggressive way to treat symptomatic patients is to perform a heart transplantation if one is a candidate for one.
Well first off i can say to you that if the person whom you are reffering to can indeed play tennis, walk upstairs etc then his/her heart is NOT as weak as you say. Has this person had a thorough examination? Is he/she under the cardiologists care? Seeing the nature of the question i don't think he/she is.
In answer to your question, it really all depends on the severity of heart failure the person is suffering from. This can be from a change in lifestyle with medication to a heart transplant. But let me assure you that if the person is in need of a transplant there is NO way that person will be able to play tennis or walk up a flight of stairs. They will be breathless most of the time and will be bedridden and need oxygen to support their circulation.
Hope this has been of help, but my advice would be to seek out proper professional advice where the patient can be assessed and monitored and you can have a full explaination of the treatment and disease.