What is the cardiac cycle?

The cardiac cycle is what happens during a single heartbeat.

To understand the cycle it helps to know that the heart is made up of four chambers, the top 2 chambers are called the atria and the lower 2 chambers are called the ventricles. Veins carry blood towards the heart and arteries take blood from the heart to the rest of the body.

Blood flows into the atria and this blood is pushed down into the ventricles, the ventricles contract and squeeze blood from the ventricles into the connecting arteries (the aorta and the pulmonary artery). To stop any blood flowing the wrong way there are valves which snap shut when the ventricles contract. The atria start to fill again and the whole cycle starts over.