And as we begin running quicker, what that means is the heart has to pump quicker and more and with a more forceful contraction. And so what that happens is it also needs to actually create ATP molecules and the lactate molecules basically create this additional source of energy that can be used to basically form that glucose, to form the pyruvate that is actually then fed into the mitochondria. So lactate goes into the cardiac muscle cell which is transformed by lactate dehydrogenase into Pyruvate and then the Pyruvate goes straight into the mitochondria. Why? Well, because cardiac muscle cells never undergo anaerobic respiration. There's always plenty of oxygen inside the cardiac muscle cells.