The Beating Heart

The right side of the heart contains deoxygenated blood received from the body, and it is pumped from the heart toward the lungs. The left side of the heart contains oxygenated blood from the lungs, which is pumped out to supply the body's tissues.

Recognize that blood flows simultaneously into the top two chambers of the heart (the atria). The atria contract in unison to pass blood through the atrioventricular valves (more commonly referred to as A-V valves) and then pass blood into the ventricles. The ventricles also contract synchronously to push blood from the heart.

The signal that triggers a heartbeat begins in the sinoatrial (SA) node which stimulates the cardiac muscle cells to contract and relax rhythmically. The message from the SA node transmits a signal to the atrioventricular (AV) node which signals the Purkinje fibres. The pumping action (muscle contraction/relaxation) is coordinated by these Purkinje fibres (or Purkyne tissue) located in the inner ventricular walls of the heart, just beneath the endocardium or lining of the heart chambers. These fibres are specialized myocardial fibres that conduct an electrical stimulus or impulse that enables the heart to contract in a coordinated fashion.