1. Heart and Cardiac cycle
Revision

3. Left or right Which side of the heart contains oxygenated blood?
Which side of the heart receives blood returning from the body?
Which side of the heart pumps blood to the lungs?
Which ventricle has thicker muscle walls?
Which ventricle pumps the highest volume of blood?
Which ventricle pumps blood into the aorta?

4. The cardiac cycle This is the series of events in one heart beat.
Each heart beat lasts about 0.8 seconds so the cardiac cycle repeats about 70 times in one minute.
The three stages are atrial systole, ventricular systole and diastole

6. Now for the graph

7. Control of the cardiac cycle
Electrical impulses sent out from the SAN stimulate the atria to contract.
The right atrium contracts marginally before the left because the SAN is situated in the wall of the right atrium.
The electrical impulses spread across the right atrium first, then the left.

8. Control of the cardiac cycle
The tissue separating the atria from the ventricles does not conduct electrical impulses so the wave of excitation cannot move down to the ventricles.
There is another node at the top of the septum where it joins the right atrium, the AVN.
This is triggered by the electrical impulse from the SAN, it then pauses the signal to allow the ventricles to fill fully before they contract.

9. The ECG picks up electrical impulses in the heart

10. Questions
What happens to the pressure in the ventricles when the ventricles contract?
What causes the semilunar valves to close?
What causes the atrioventricular valves to open?
What starts a heart beat?
Describe the spread of the electrical impulse through the heart.
In the ECG what is represented by the P wave? And the QRS complex?