The Heart
Heart Chambers
Each side of the heart comprises 2 chambers - the upper chambers are the atria, and the lower chambers are the ventricles. The left and right sided chambers are separated by a wall of muscle, called septum.

The right sided chambers deal with receiving deoxygenated blood from the vena cava, and sending it to the lungs, via the pulmonary arteries. The left sided chambers receive oxygenated blood from the lungs, via the pulmonary veins, then pump the blood into the aorta, to be delivered to the systemic circulation.

Heart valves:
TricuspidRegulates blood flow between the right atrium and right ventricle.
PulmonaryControls blood flow from the right ventricle into the pulmonary arteries, which carry deoxygenated blood to the lungs.
BicuspidAka the Mitral valve, lets oxygenated blood from the lungs pass from the left atrium into the left ventricle.
AorticAllows oxygenated blood to pass from the left ventricle into the aorta, from whence it is distributed to the whole body.
Cardiac Cycle

Electrical activity in the heart follows the Cardiac Cycle...
  1. The Sinoatrial Node (pacemaker) in the right Atrium creates an electrical signal.
  2. The electrical signal flows through both Atria, stimulating the Atria to contract and push blood into the ventricles.
  3. When the electrical signal reaches the Atrioventricular Node, it pauses to give the ventricles time to fill with blood.
  4. The electrical signal spreads through the Bundle of His, then to the Purkinje Fibres, which are located in the cardiac muscle. This causes the ventricles to contract and push blood out to the pulmonary and systemic circulations.