Cardiac Cycle




We will cover the following in class. But you could work with this a little on your own to see how you do. The important principle is that the heart valves open and close due to pressure differences. When the pressure is greater on the upstream side of a valve, the valve leaflets open. When the pressure is higher on the downstream side of the valve, the valve leaflets close.

To the right are tracing of the pressures that determine the opening and closing of the valves on the left side of the heart. The mitral valve lies between the left atrium and the left ventricle. The aortic valve lies between the left ventricle and the aorta. The right side would be similar, except the pressures are 1/7 as large.

The top graph shows the pressures that determine the opening of the left atrioventricular valve:

The bottom graph shows the pressures that determine the opening of the aortic valve:

The vertical line indicates when an action potential travels over the ventricles, triggering their contraction.

On these graphs, identify when the left atrioventricular valve opens and closes and when the aortic valve opens and closes. When is the first heart sound and when is the second heart sound?




On the right is shown a graph with all three pressures. Lines indicate the times of the opening and closing of the valves. On the graph, you will want to identify the specific phases of the ventricular systole and diastole and understand what is occurring in each phase. The phases are:


If you like, you can download a worksheet to practice learning the phases of the cardiac cycle.

Finally, try the quiz below.




Quick Quiz

Fill in Answer Correct False Correct Answer
What valve closes at the very beginning of isovolumetric contraction?
What valve opens at the very end of isovolumetric contraction?
What specific phase begins immediately after the R wave in the electrocardiogram?
What phase of ventricular diastole begins at the point when the atrial pressure first becomes greater than the ventricular pressure?
What specific phase begins with the closing of the aortic valve?
What specific phase begins with opening of the aortic valve?
What specific phase begins when the ventricular pressure falls below the aortic pressure?
What specific phase occurs immediately before isovolumetric contraction.

(Spelling must be correct)
OK, Go ahead and give me: