Multicellular organisms need to be fed and maintained and require pathways around the body for these processes to take place. In the human body, we have the circulatory system, or "cardiovascular" system which acts both as a delivery mechanism for such things as oxygen, it also doubles as a waste collection service to help us to dispose of things like carbon dioxide.


The human cardiovascular system is a double circuit system. One of the circuits is responsible for taking oxygen around the body and collecting waste products such as carbon dioxide which will then return to the heart. The other system will take the carbon dioxide rich blood back to the lungs where it will be exchanged for oxygen, the carbon dioxide will be expelled from the lungs and the freshly oxygenated blood will return to the heart to start the cycle all over again.


This highly efficient two circuit system is controlled and coordinated by the heart, an efficient fluid exchange system within the heart ensures that the right substances go to the right place to be directed accordingly.



1. Starting at the LUNGS, oxygenated blood enters the HEART through the PULMONARY VEIN, arriving in the LEFT ATRIUM.


2. From the LEFT ATRIUM the blood is pushed via muscular contraction through THE MITRAL, OR BICUSPID VALVE into the LEFT VENTRICLE.


3. Muscular contraction forces the blood out of the LEFT VENTRICLE through THE AORTIC VALVE into the AORTA and off to the rest of the BODY.


4. Deoxygenated blood returns to the heart from the SUPERIOR and INFERIOR VENA CAVA, entering the RIGHT ATRIUM.


5. Muscular contraction forces the blood through THE TRICUSPID VALVE into the RIGHT VENTRICLE.


6. Muscular contraction pushes the blood through THE PULMONARY VALVE out into the  PULMONARY ARTERY where it returns to the LUNGS.


In each side of the heart, there are valves which operate in one direction only. This is to make sure that there is no back flow or back pressure which could compromise a beat and affect the flow of blood around the body.

On the left-hand side of the heart, lying between the left atrium and left ventricle we have the "bicuspid" or "mitral" valve which opens to allow blood to flow from the atrium into the ventricle, but then closes again when the ventricle compresses to send the blood through the aorta.


As the mitral valve closes, the left ventricle compresses forcing the blood up through the "aortic valve" and out through the aorta, the aortic valve then closes to allow the mitral valve to reopen, allowing more blood to flow from the left atrium to left ventricle.

On the right-hand side of the heart, again separating (this time) the right atrium from the right ventricle is the "tricuspid" valve. In the same way as for its counterpart on the left-hand side, it opens to allow blood to leave the atrium and enter the ventricle, but then closes again when the right ventricle contracts, pushing the blood out into the pulmonary artery.


The tricuspid valve closes, which allows the right ventricle to contract, this pushes blood through the "pulmonary valve" and out into the pulmonary artery. The pulmonary valve then closes which allows the tricuspid valve to open, refilling the right ventricle with blood from the right atrium.


Considering that your heart beats, at its "rest rate" of around 72 bpm, your heart will clock up .....


..... beats in a day, which makes your heart one of the busiest things you own!