This document summarizes a lab experiment where students observed how heart rate and rhythm change when a person is relaxed, seated, and after exercising. It describes the basic anatomy of the heart, including its location in the chest and its division into two circuits - the pulmonary circuit which carries blood to and from the lungs, and the systemic circuit which carries blood to and from the rest of the body. It provides details on the flow of blood through the different chambers and valves of the heart in each circuit.