The cardiac muscle in the heart is myogenic, thus allowing it to keep its pace. There is a septum dividing the two circulations from each other in the heart, this allows for there to be pumping chambers (or two ventricles.) Each ventricle pumps to its own circulation. But the left ventricle is more muscular than the right. Thus this allows for higher pressures to be built in the left ventricle, therefore blood can be pumped around the whole body by the left ventricle. The right ventricle is less muscular as it only has to build up enough pressure to pump blood to the lungs.
Step-by-step explanation: