Cardiac impulse is the electrical signal in charge of coordinating the contractions in each individual muscle fiber in the heart. This signal is triggered by a tiny natural pacemaker in the right atrium of the heart which sets off electrical impulses to the four chambers that make up the heart. This lays out a sequence for the four chambers to contract and relax in an orderly fashion. Each contraction of the heart has a specific purpose; it pumps blood throughout the body as well as back to the heart to allow for the cycling of oxygen and nutrients. Without this rhythm the heart can't pump effectively.