The Cardiac Cycle

Systole – contraction Diastole – relaxation PLEASE SEE THE HANDOUT ON THE WIKI FOR DETAILS OF EACH STEP

Atrial ventricular diastole – – Blood enters the atria – Tricuspid and mitral valves are closed Atrial systole / Ventricular diastole – blood is pumped from the atria to the ventricles – Tricuspid and mitral valves are open, pulmonary and aortic valves are closed Atrial diastole / Ventricular systole – Blood is pumped from ventricles out of the heart through the aorta and pulmonary artery – Tricuspid and mitral valves are closed, pulmonary and aortic valves are open

SA Node – sinoatrial node – Located in the right atria – The hearts natural pacemaker – Generates an electrical impulse which spreads through the muscle fibers in the atria – Atria contract AV Node – The electrical impulse from the SA node is picked up by the AV node – Delay of electrical impulse – The impulse is then spread through the walls of the ventricles, leading the ventricles to contract