So during the generation of an action potential inside a cardiac muscle cell, we have this extended period of depolarization that is caused by the presence of voltage gated calcium channels inside the membrane of the cell. So the membrane of the cell doesn't only contain sodium and potassium voltage gated channels, it also contains calcium voltage gated channels. So let's see what happens. So our resting potential is about negative 90 millivolts. And let's suppose we have some type of stimulus that reaches the threshold voltage of about negative 70 millivolts. So what happens next?