How The Heart Works

1
How The Heart Works
2
Inside the Heart

• The heart has four hollow chambers inside.
• The two upper chambers are called atria. Each is
  an atrium.
• The walls of the heart are made of cardiac
  muscle.
• The wall down the middle is called the septum.
  It divides the heart into two parts.
• The two lower chambers are called ventricles.

3

• The are two semilunar valves stop blood flowing
  back into the heart from the arteries.
• There are two valves that stop blood flowing back
  into atria from the ventricles.
• The other valve is called the biscupid or mitral
  valve.
• The final valve is called the tricuspid valve.

4
The Cardiac Muscle

• The walls of your heart are made of cardiac
  muscle.
• When this contracts the heart gets smaller so
  blood gets pumped out.
• The right side pumps deoxygenated blood to the
  lungs, at a low pressure.
• The left side pumps oxygenated blood all round
  the body, at a much higher pressure. This needs
  more force, so the left side has thicker walls.
• The left ventricle has the thickest walls,
  because it works hardest of all.
• When it contracts, it pumps blood into the aorta
  and round the body.

5
How the heart pumps blood

• (1) When the heart is relaxed, both sides fill
  with blood from the veins. (but no blood can flow
  in from the arteries).
• (2) The atria contact. The veins contract where
  they join atria. So blood from the atria is
  forced into the ventricles.

• (3) Then the ventricles contract. The valves
  between the ventricles and atria close. So the
  blood is forced out of the heart, into the
  arteries.
• (4) The heart muscle relaxes again and steps 1
  3 are repeated.

6

• This cycle of events is called the cardiac cycle.
• One complete contraction and relaxation is called
  a heart beat.
• Your heart beats around 70 times a minute when
  you are resting (less if you are fit).
• This can rise to 200 beats a minute when you run
  very fast.
• The number of beats per minute is called your
  heart rate.