If you are talking about muscle cells, I am not sure you are going to be able to find a company that cells cardiac muscle cells, and even if they did, they would not be usable for more than one passage.  I isolate neonatal rat heart cells for experiments from pups less than one week old using a kit from worthington biochemicals.  I get a terriffic yield and can maintain cultures of beating cells in dishes for more than a month, however, they do not double more than once after isolation, if that, and they generally do not reattach after passaging, so you must plate them for the deisred experiment at the time of isolation, and you get what you get.  Adult cardiac muscle cells can be isolated with the same kit, but they will not attach to plates and must be used immediately, as they die within hours.  Skeletal muscle cells can generally be sub-cultured for a few passages, but I have no experience with them. 

Good luck

Thanks alot!! This is very helpful