Can my job fire me if I am at home on disability from a heart attack?

I have 6 heart attacks since 2006 and an tribple bypass last year and this year 4 heart attacks. I am not fully better and have been home since Marach 30. My fmla will run out soon. Can my employer fire me? I am currently on short tern disability throught my job and wondering if I will have a problem getting into long term and still hold my job until I am better. I am aware my employer must fill my position in the mean time. I have relapses and returned to work. so this time my doctor wants to ensure I am absolutely stable before I return to work and had another heart attack and not knowing what the turn out can be. Last heart attack I almost did not make it so I am scared to even ask to return to work if I am not stable without symptoms for at least 2 to 3 months. If I get six months out will I get fired?