Heart science

1. The heart is a fist-sized muscular organ that sits in the chest cavity.
What does your heart do?
The purpose of your heart is to pump blood to the organs and tissues of your body that need the
oxygen and nutrients it carries. Oxygen-rich blood is pumped out of the left side of your heart (shown
on the right in the diagram) into the arteries to these tissues and organs.
Blood that has delivered its nutrients and oxygen and is in need of oxygen comes back to your heart
in the veins and enters the right hand side of the heart (on left of diagram). This blood which is in
need of oxygen (so-called deoxygenated blood) is sent to your lungs to pick up oxygen and get rid of
carbon dioxide.
Your heart pumps all day to circulate blood around the body. On average, a red blood cell in the
circulation will pass through the heart every 45 seconds. If you start to exert yourself your heart will
start to pump faster to supply your working muscles with the increased amount of oxygen and
nutrients they need. The heart is a muscle too, and to enable it to pump effectively, it has its own
blood supply bringing it oxygen.
How does your heart work?
Your heart is made up of 2 pumps. The pump on the right hand side receives blood that has already
delivered its oxygen round the body and sends this blood to the lungs to pick up more oxygen (and
get rid of carbon dioxide).
The pump on the left hand side receives oxygen-rich blood and then pumps it out into the arteries to
deliver its oxygen around the body.
Blood in need of oxygen enters heart
Blood in need of oxygen from around the body travels in the veins to the heart. This blood in need of
oxygen (also called deoxygenated blood) is usually shown as blue or purple on diagrams.
This ‘deoxygenated’ blood enters the top right hand side chamber (shown on left in diagram) of the
heart, which is called the right atrium, via two large veins. Blood from the upper body, e.g. the head
and arms, comes in via the superior vena cava. Blood from the lower body, that is the trunk and
legs, comes in via the inferior vena cava.
Blood passes from right atrium to right ventricle
When the right atrium fills, the blood then passes through a one-way door (valve) called the tricuspid
valve into the right ventricle. The valve stops blood from flowing backwards into the right atrium once
it’s in the right ventricle. The right ventricle relaxes and venous blood in need of oxygen flows in.
Right ventricle sends blood needing oxygen to the lungs
The blood needing oxygen is pumped out of the right ventricle, through the pulmonary valve into the
pulmonary artery. The pulmonary artery then divides into the right and left pulmonary arteries,

2. carrying blood to the right and left lungs. In the lungs the blood gives up its carbon dioxide and picks
up oxygen.
Oxygen-rich blood from lungs enters heart
Fresh blood full of oxygen leaves the lungs and comes back to the heart in the pulmonary veins.
This oxygen-rich blood enters the left atrium — the top left chamber of the heart (on right of
diagram).
Blood passes from left atrium to left ventricle
When the left atrium is full it pushes the blood through the mitral valve into the left ventricle.
Left ventricle sends oxygen-rich blood around body
The left ventricle relaxes and fills up with blood before squeezing and pumping the oxygen-rich blood
through the aortic valve into the aorta — the main artery that carries blood to your body. The muscle
wall of the left ventricle is very thick because it has to pump blood around the whole body.