The electric heart

The heart has a natural pacemaker that regulates the rate and pace of the heart. This pacemaker sits on the upper portion of the right atrium and consists of a collection of special electrical cells known as the sinus or sino atrial (SA NODE). The SA node generates electricity which travels across a special pathway to stimulate the muscles of the four chambers of the heart to contract in a specific way.

The heart usually beats about 72 beats per minute on average at rest (normal activity) and is part of an intricate series of events that happen within your heart to produce a heartbeat. Each heartbeat consists of two parts.

• Diastole is where the atria and ventricles relax and fill with blood.



• Atrial is where the atria contracts and pumps blood into the ventricals. The atria relaxes so your ventricles can then contract pumping blood out of the heart.

As mentioned the electrical signal that sets the heart pumping begins with the SA node which then generates the two vena cavae to fill the hearts right atrium with blood from other parts of the body. This signal then spreads right across the cells of the heart to the right and left atria causing the atria to contract. This contraction then produces the action to push the blood through to the open valves from the atria into both the ventricles. The signal arrives at the AV node which sits near to the ventricles slows for an instant which allows the right and left ventricles of the heart to fill with blood. The signal is then released, moves along a pathway called the 'Bundle of His' (which is a collection of heart muscles cells specifically for the conduction of electrical activity which then transmits electical impluses from the AV node to the point of the apex of the fascicular branches) located within the walls of the ventricles.

From the 'Bundle of His' the signal fibers then divide to the right and left bundle branches through the Purkinje fibres which connect directly to the cells within the left and right ventricles. The signal then starts to spread acroos the these cells causing both ventricles to contract, which however doesn't happen at exactly the same time. This is because the left ventricle contracts an instant before the right one does. By doing this it pushes the blood through the pulmonary valve situated at the right ventricle to the lungs, then through the aortic valve for the left ventricle to the rest of the body.

As the signal passes the walls of the ventricles relax and await the next coming signal so the whole process continues over and over again.