These valves closed and the right and left atrium are now relaxing. Now, the question is why exactly is the voltage difference here so high? Well, that's because this section of the heart, the ventricles, contain the thickest layer of myocardium. They have the thickest layer of muscle cell. And so that means a much higher voltage difference is needed to cause the contraction of all these muscles found within our right and left ventricle. And that's exactly why this peak is such a high peak.