Cardiac Cycle

Cardiac Cycle

Heartbeat phases that pumps blood through the body by coordinating heart muscle contractions and relaxation

• Contraction and relaxation of atria 

• Systole and diastole of both ventricles 

Systole

contraction

Diastole

relaxation

Step 1?

Atrial Systole

Atrial Systole

• Atria Depolarization triggers Atria systole (contraction) (P wave) → push last 20% of blood

Step 2?

Isovolumetric contraction

Isovolumetric contraction

• Atria relaxes = Ventricles start contracting

• ALL AV valves closed

• Ventricles continue to contract

• Ventricular Pressure Too Much = SL Valves OPEN

Step 3?

Ventricular ejection

Ventricular Ejection

SL valves open → blood leaves heart into arteries 

Isovolumetric relaxation

• Ventricles relax

• ALL valves closed again

Ventricular Filling

AV valves open → blood flows in (80% passive from atria through open AV valves in ventricles)

Step 4?

Isovolumetric relaxation

Step 5?

Ventricular Filling