The cardiac cycle

• What is cardiac cycle?

  sequence of events that take place in a complete

  heart beat
• What happens during this process?

  One complete cycle of pumping and filling blood into the heart occurs.
• One complete cardiac cycle lasts for?

  0.8 seconds
• What are the steps of the cardiac cycle?


  Atrial systole - contraction of the atria

  Ventricular systole - contraction of the ventricles

  complete cardiac diastole - relaxation of the atria and ventricles
• At rest the healthy adult heart is likely to beat at a rate of?

  60 - 80 beats per minute
• What happens during a single heart beat?

  The heart contracts (systole) and then relaxes (diastole)
• What is called as the stroke volume?

  During a single contraction the amount of blood pumped by a ventricle
• How is the process of the atrial systole?


  When blood flows into the atrium the SA node is stimulated. The electrical impulses generated in the SA node , trigger a wave of contractions that spread over the myocardium of both atria.

  Hence the remaining blood in the atria flows into the ventricles thereby emptying the atria.
• Atrial systole lasts for?

  0.1 seconds
• How do electrical impulses reach the AV node?

  Through the atrial muscles
• What allows the atria to finish emptying to ventricles before it starts to contract?

  Atrioventricular transmission is delayed ( by a fraction of a second) at the AV node
• What happens after this delay?


  AV node triggers its own electrical impulses which quickly spread to the ventricular muscles via the AV bundle, the bundle branches and purkinje fibers
• What happens a result of those impulses?


  Wave of contractions which sweep upwards from the apex of the heart across the wall of the ventricles. As a result both ventricles contract
• Why does pulmonary valve and aortic valves open and blood flows into pulmonary artery and aorta respectively?


  The pressure in the right ventricle is more than the pressure in the pulmonary artery and the pressure in the left ventricle is more than the pressure in the aorta.
• What force atrioventricular valves to close?


  The high pressure generated during ventricular contraction
• What is the importance of closing atrioventricular valves ?

  preventing backflow of blood into the atria
• Ventricular systole lasts for?

  0.3 seconds
• What happens when the ventricles relax?


  The pressure within them falls. The pulmonary and aortic valves close
• Pressure within the pulmonary artery and aorta is more than the?

  pressure within the ventricles
• The valves of the heart and great vessels open and close according to what?

  Pressure within the chambers of the heart
• The sequence of opening and closing of valves ensure what ?

  That blood flows only in one direction
• Complete cardiac diastole lasts for?

  0.4 seconds
• What happens during complete cardiac diastole?


  Both atria and ventricles relaxed and blood return to the heart. The superior and inferior vena cava transport oxygen poor blood into the right atrium. at the same time as the four pulmonary veins bring oxygen rich blood into the left atrium
• Why are atrioventricular valves are open and some blood flows passively through the ventricles?

  The pressure of the atria is more than the pressure of ventricles