And that is a problem because the cells need oxygen to produce ATP molecules in an efficient way. And these ATP molecules are used as energy molecules to carry out all the different types of processes that take place inside the cells and inside our body. Now, what our body does immediately is it increases the rate at which we breathe, so it increases the ventilation rate. And this is known as hyperventilation. And it also puts stress on the heart by increasing the rate at which the heart actually pumps. Now, although these are useful immediately, they're not very useful in the long term because this puts a lot of stress on the heart.