phases of the Cardiac Cycle

KINS 256 – Cardiovascular Worksheet

Complete the following worksheet by responding to the prompts. Each prompt is worth 2 points.

1. Outline the flow of blood through the heart.

2. List and explain the phases of the Cardiac Cycle including how the SA node, AV node and Purkinje fibers aid in control of this process.

3. Define Cardiac Output and provide the equation that is used to determine this.

4. Explain what would happen to stroke volume if EDV increases and ESV remained constant or decreased.

5. Pretend you have a client that asked you to explain to them why regular exercise can help lower their blood pressure.

6. What changes would you expect to see in a person’s HR, SBP and DBP respectively, in response to exercise?

7. Discuss what VO2 is, including the components of the equation used to calculate this. Discuss the expected difference in VO2 max for trained vs. untrained individuals including why you would expect to see that difference.

8. Discuss the physiological adaptations to the Cardiovascular system during exercise (Don’t just list, discuss briefly how each responds).

9. From a physiological perspective, what concerns might you have if an athlete’s labs indicated their hematocrit values were low. What could this mean, and why could this impact training?

10. Explain the physiological processes that result in the redistribution of blood flow during exercise.

List and explain the phases of the Cardiac Cycle including how the SA node, AV node and Purkinje fibers aid in control of this process.


The cardiac cycle is a very complex process that relies on many different mechanisms to keep it going. In fact, the SA node, AV node and Purkinje fibers all have their own unique roles in this process. The SA node controls the resting potential of the heart and is responsible for ensuring that the membrane potential remains unchanged after each beat. The AV node does just what its name implies—it controls the conduction of electrical impulses through the AV-Drain system (which consists of specialized channels located between cells called gap junctions). Finally, the Purkinje fibers conduct impulses from tissue to tissue by conducting them through dendrites while following an action potential down into muscle cells where they are stored in special “somatic” memory cells known as “sarcoplasmic reticulum.”

Phase 1: Resting Potential

The resting potential is a state of equilibrium between the ions inside and outside of a cell. The resting potential is -70mV, which means that there is no net movement across the membrane. This means that if you place an electrode on a nerve or muscle you will not get any current flowing through it because there are no ions leaking out of your body’s cells (unless they are already being pumped out).

The membrane itself does not have any pores; it’s permeable only to Na+ and K+.

Phase 2: Depolarization

Phase 2: Depolarization is the second phase of the cardiac cycle. In this phase, the SA node triggers conduction through the atria, while AV nodal function slows down this process (for more details on what these terms mean, see our later section). Purkinje fibers speed up conduction through the ventricles.

Phase 3: Repolarization

The final phase of the cardiac cycle is repolarization. During this phase, the membrane potential is restored back to its resting value by opening of voltage gated calcium channels and sodium channels.

As we discussed above, there are several different types of cells that make up your body. These cells have specific functions within the body and they all work together to keep you alive!

Phase 4: Absolute Refractory Period (ARP)

The absolute refractory period (ARP) is the phase of the cardiac cycle when myocardial cells are unable to respond to a new stimulus. The duration of this phase varies between individuals and can range from 30-60 seconds, depending on the stimulus and amount of time it has been present.

The second fastest phase of this cycle occurs during Phase 4 – Absolute Refractory Period (ARP), which lasts around 40 milliseconds.[1] This means that although you may feel like you have already responded to something before you realize it’s still happening!

The cardiac cycle is a very complex process that relies on many different mechanisms to keep it going.

The cardiac cycle is a very complex process that relies on many different mechanisms to keep it going. The cardiac cycle is the sequence of events that occur between the time a heart cell is stimulated and the time it contracts.

The first phase in this process involves your heart’s electrical system, which sends signals from your nervous system to individual muscle cells that contract certain groups of muscles within your body (the SA node). This causes them to squeeze blood out into arteries around your body so that it can flow through these vessels until they reach their destination–your lungs where oxygen-rich air enters through tiny holes called endothelial tubes (tiny holes inside capillaries). Then oxygen enters these capillaries as well and travels down into red blood cells before returning back up into arteries again!


In this article we’ve covered the basic function of the SA node and AV node and how they are related to the heart’s pumping action. The next step is to understand how these electrical signals reach your cells, which is why it’s so important for you to stay informed about what goes on inside your own body!

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