Humans have two circulatory system, i.e. a high-pressure system (i.e., the arterial circulation) and a low-pressure system (i.e., the venous circulation), each with a separate cardiac chambers or “pumps” (Fig. 1.1). This pump includes, on the right side (low-pressure system with predominantly low oxygen content) and the left side (high-pressure system with high oxygen content), an atrium and a ventricle, each separated by four heart valves that function as valves.