Why? Well, because cardiac muscle cells never undergo anaerobic respiration. There's always plenty of oxygen inside the cardiac muscle cells. And so for that reason the Pyruvate is fed directly into the mitochondria. So we see that these cardiac muscle cells really utilize these high energy molecules because not only do the glucose molecules inside the cardiac muscle cell actually transform into Pyruvate and then go into the mitochondria. And not only are the glycogen storages used to produce the glucose six phosphate which ultimately form the ATP molecules, but in addition the lactate molecules produced by the other cells that undergo anaerobic respiration are also used to actually form these energy molecules.