The heart is comprised of four chambers: two upper atria, and two lower ventricles. An electrical system controls the synchronized pumping action of these chambers.
The normal heartbeat originates in a section of the right atrium known as the sinoatrial, or SA node. The electrical signal from the sinoatrial node spreads through both atria causing them to contract and squeeze blood into the ventricles. The electrical signal then passes through an electrical bridge known as the atrioventricular or AV node. After a split second delay, the signal continues to the ventricles by way of a specialized network known as the left and right bundle branches.
The bundle branches separate to the left and right ventricles, which enables the electrical signal to stimulate both ventricles simultaneously. This coordinated contraction, or squeezing, of the ventricles is necessary for optimal pumping of blood to the body and lungs.