How do the heart muscle cells have the energy to keep beating?

Question: How do the heart muscle cells have the energy to keep beating?
- Keywords:
  cells,
  energy,
  heart muscle
Asked by kattypuss to Rachael, Penny, Jennifer, Jean-Paul, David, Dave on 6 Jan 2014.
- Penelope Mason answered on 6 Jan 2014:
  
  Cardiac or heart muscle is actually specially adapted so it only needs to rest between beats. Basically heart muscle cells are stuffed full of mitochondria so they can produce LOTS of energy quickly, and the mitochondria themselves are more efficient than mitochondria elsewhere. The heart also has an extremely rich blood supply so it can get nutrients very quickly and also get rid of waste products fast.

Question: How do the heart muscle cells have the energy to keep beating?