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The cardiac cycle. Describing the sequence of events in one heart beat. Learning Intentions. Describe the cardiac cycle with reference to the action of the valves in the heart. Introduction.

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The cardiac cycle

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the cardiac cycle

The cardiac cycle

Describing the sequence of events in one heart beat

learning intentions
Learning Intentions
  • Describe the cardiac cycle with reference to the action of the valves in the heart
  • It is important that the chambers of the heart contract in a coordinated fashion. The sequence of events involved in one heartbeat is called the cardiac cycle.
  • Systole = period of ventricular contraction.
  • Diastole = period of ventricular relaxation.
  • NOTE:  Normally diastole is longer than systole.
cardiac cycle
Cardiac cycle
  • General Principles.
  • Contraction of the myocardium generates pressure changes which result in the orderly movement of blood.
  • Blood flows from an area of high pressure to an area of low pressure, unless flow is blocked by a valve.
  • Events on the right and left sides of the heart are the same, but pressures are lower on the right.
atrial systole
Atrial systole
  • The heart is full of blood and the ventricles are relaxed
  • Both the atria contract and blood passes down to the ventricles
  • The atrio-ventricular valves open due to blood pressure
  • 70% of the blood flows passively down to the ventricles so the atria do not have to contract a great amount.
ventricular systole
Ventricular systole
  • The atria relax.
  • The ventricle walls contract, forcing the blood out
  • The pressure of the blood forces the atrio-ventricular valves to shut (producing the heart sound ‘lub’)
ventricular systole1
Ventricular systole
  • The pressure of blood opens the semi-lunar valves.
  • Blood passes into the aorta and pulmonary arteries.
  • The ventricles relax
  • Pressure in the ventricles falls below that in the arteries
  • Blood under high pressure in the arteries causes the semi lunar valves to shut. This produces the second heart sound, ‘dub’.
  • During diastole, all the muscle in the heart relaxes.
Blood from the vena cava and pulmonary veins enter the atria.
  • The whole cycle starts again.







Cardiac cycle

= 0.8 sec

60/0.8 bpm

= 72 bpm


A Atrioventricular (bicuspid / mitral) valve(s) closes (“snaps shut”– makes 1st louder heart sound “LUB”

B Semilunar valve(s) (aortic valve) opens

C Semilunar valve(s) closes – makes second softer heart sound “DUB”- shut due to blood accumulating in their pockets

D Atriioventricular (bicuspid) valve(s) opens

cardiac cycle1
Cardiac cycle

Match the letter on the graph to the following events


Length of 1 cardiac cycle ~ 0.8 sec

No of beats per minute = 1 x 60/0.8 sec = 75 beats/min