Cardiovascular Physiology: Preload and Afterload

What is the difference between preload and afterload? This is one of most frequently asked questions and probably one of the most confusing topics that nursing students encounter during their lectures and clinical rotations.

To settle the confusion once and for all, we will provide you with the most uncomplicated answer.

The Slingshot Analogy

The heart is an intricate organ that causes quite a bit of bewilderment, especially with nursing students. And one of the topics that bring about such confusion is concerned with preload and afterload.

Consider this analogy – the heart is like a slingshot; a slingshot that requires pressure when pulling and energy upon release.

Preload: The Pulling Effect

The pulling action of the slingshot is called preload. Preload occurs so that there will be the pooling of blood that will either be pushed into the lungs or to the rest of the body. Preload is also referred to as the diastolic pressure inside the blood vessels.

Afterload: The Release

Afterload, on the other hand, is the action when the slingshot is released. Basically, afterload is the amount of pressure that the heart has to overcome to enter the next phase, whether the blood will go inside the lungs or the peripherals. Afterload is also known as the systolic pressure inside the blood vessels.

Quick Anatomy and Physiology

The heart has four chambers – right and left atria, and right and left ventricles. These chambers are also considered as rooms that have vital roles in the distribution and oxygenation of blood to various parts of the body.

Deoxygenated blood is received by the right atrium from the body and is pushed to the lungs by the right ventricle to be filled with oxygen. The left atrium will receive the oxygenated blood and will send it to the left ventricle. The left ventricle will distribute the oxygen-rich blood to the rest of the body.

Between the atria and the ventricles, the ventricles are considered as the essential rooms inside the heart because they’re responsible for the pulling and pushing of blood to the body.


So just remember this:

  • Preload – the stretching or pulling to fill the heart with blood
  • Afterload – the release or push of oxygenated blood by the left ventricle to the lungs and the rest of the body

That’s it for our simplified preload and afterload explanation that was brought to you by, the best student nurse website that has helped more 40,000 students all over the world.

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Cardio-Physiology Pt 1: Intro to our body’s Pumping Station

Cardiovascular physiology is primarily focused on getting to know the basic structures of the heart, how these structures work, and what areas are involved in electrical conductivity.

Functions of the Cardiovascular System

Realizing the main functions of the cardiovascular system is necessary for understanding the physiology of the body. With the heart’s intricate pathways of capillaries, arteries, and veins, pumping of oxygen-rich blood, which is one of the primary responsibilities of the cardiovascular system, throughout the body’s entire system is made possible.

Aside from keeping a steady flow of oxygen in the body, the heart and its vessels also perform the following:

  • Transport essential nutrients
  • Remove metabolic toxins and wastes
  • Regulate normal temperature

For more information about how blood flows and distribute oxygen throughout the body, we have prepared a separate video dedicated entirely to that topic. Check it out on our channel.

Hotel Cardiac

Keep in mind that the anatomy portion is different from the electrical part of the heart. So, inside the heart, there are four main chambers, namely:

  • Right atrium
  • Left atrium
  • Right ventricle
  • Left ventricle

We explain every single chamber in a song we’ve created titled, Hotel Cardiac. This is basically a spinoff of the popular song, Hotel California. You can also check the lyrics of that song in our channel so it would be easier for you to memorize and recall how the electrical portion of the cardiovascular system works.

The Rooms

Going back to the Hotel Cardiac song, think of the heart as a four-bedroom suite. Let’s identify each room and what their functions are.

  1. Atriums

As mentioned, the heart has four rooms or chambers, and at the upper portion, there are the attics or what we call as atriums. Atriums are considered as attics because they are comparably smaller than ventricles. These atriums are the receivers of blood either from the rest of the body or the lungs.

  1. Ventricles

Located just below the atriums, the ventricles are the suites of the hearts because they are relatively larger due to their principal objective which is to pump blood to the lungs and out of the heart to the rest of the body. The biggest between the left and right ventricle is the left ventricle which is tasked to pump all the oxygenated blood throughout the various systems. Therefore, if the left ventricle is compromised, the body is doomed.

The Doors

In each of the four bedrooms inside the heart, there are doors which we call valves. These valves are automatic doors that allow blood through the various rooms or suites inside Hotel Cardiac. The sounds, “lub dub,” that are heard when a heart is auscultated are the valves closing.

The Cardiac Gang Sign

The cardiac gang sign, which is just the right hand forming an L like a gun or a loser sign, is a technique that is used to determine the location of the tricuspid and bicuspid valves. By forming an L-shaped figure with your thumb and index finger and closing the rest of the fingers, place the cardiac gang across the chest. Here, you’ll identify that there are two valves at the left side of the heart that is known as the bicuspid valves. On the right side of the heart is where the tricuspid valves are located, which is represented by the three closed fingers.

The Pulmonic and Aortic Valves

The pulmonic and aortic valves create the fundamental sounds that are heard inside the heart. These doors operate through electrical conduction. Currently, the heart is utilizing electricity being transported by the valves.

With that in mind, why is the body not electrocuted? Because the heart is equipped with a zip-lock bag referred to as the pericardium that makes sure electricity flowing inside the heart does not leak to adjacent organs or all over the body.

In part two of our cardiovascular physiology, we will further delve into the process of electrical conduction from one valve and chamber to another. We will tackle the importance of the nodes and branches of the cardiovascular system.

For more nursing-related information that can help you pass major exams, especially the NCLEX®, visit our Simple Nursing website and check out our informative YouTube videos.

EKG Rhythms: Accurate Interpretation in 3 Easy Steps Pt 2

Whether you’ve been out of school for 30 years or more, or finishing your nursing school but still have no idea how to do proper EKG interpretation and how the concepts work, this is for you.

For anyone of you who has trouble understanding the basics, Mike has made it uncomplicated to comprehend and remember the fundamentals of EKG rhythms. Guaranteed, you’ll be able to interpret EKG rhythms in three minutes or less!

Before getting into the core of this topic, let’s focus first on what an EKG is.

EKG is short for electrocardiogram; which simply means a picture of your heart or basically the activities of your heart.

The four-bedroom suite

In, we make sure that you are able to relate every concept to what you are already familiar with. With EKG, it’s the heart. Consider your heart as a four-bedroom suite because it has four chambers and every chamber is divided by valves. These valves are like the French doors to your heart. 

The atriums

So, in the heart, there are upper rooms called atriums. The atriums are small upper chambers of the heart. These chambers, you can call refer to them as the attic or the guest rooms, they are the first ones to squeeze blood to the other chambers because the atriums are the rooms that first takes in the blood from the veins.

Remember: In all the chambers of the heart, the atriums are responsible for receiving unoxygenated blood which is blood that already circulated the body and have depleted oxygen supply.

The ventricles

Now, from the atriums, blood gets pushed down to the other chambers like the master’s bedroom or the living room. These chambers that are located below the atriums are referred to as the ventricles. 

EKG application

By keeping in mind the concept above, you can easily determine how the heart works in an EKG strip. What does each wave represent?

  • P wave – appears first, signifies your atriums pumping blood
  • QRS wave – next to appear, signifies your ventricles squeezing blood
  • T wave – relaxation or repolarization of the ventricles

So this set-up is like the principle in physics: what goes up must come down. That’s basically what you’ll see on your EKG paper.

Zooming in 

Medically speaking, the “atrial squeeze” seen on your P wave is called atrial depolarization. Depolarization is simply sending a charge away by pushing the blood out of the heart. Once the blood goes into ventricles, it takes all the blood in, making those chambers swell. The ventricles need to squeeze the blood out of their chambers which is basically your ventricle depolarization. 

After the ventricles have depolarized blood out of it chambers, it needs to re-polarize or relax. So basically your T wave is medically referred to as ventricular repolarization. 

Oxygen distribution

Here’s a quick question. Before the left ventricle has squeezes blood out of its chamber and into the aorta, where should blood go first to be oxygenated before it gets distributed to the different parts of the body?

So, here’s how the blood flows in the heart:

The right atrium receives unoxygenated blood then in pumps the blood to the right ventricle. The right ventricle is expected to be big enough to get the necessary pressure to pump the blood into the lungs. From the lungs, as we inhale oxygen and exhale carbon dioxide, blood becomes oxygenated. Oxygenated blood from the lungs goes into the left atrium and finally, it gets pumped into the left ventricle. The left ventricle, being a big chamber, is basically responsible for squeezing oxygenated blood from its area into the aorta to the different parts of the body.


Quick recap

P wave – atrial depolarization

QRS wave – ventricular depolarization

T wave – ventricular repolarization

To apply what you now know, here’s a critical thinking question:

Why isn’t there a P wave repolarization on your EKG strip (“earthquake paper” as Mike likes to call it)?

There is actually P wave relaxation; however, it doesn’t appear on your EKG strip because the QRS wave is covering it.

That’s a little trivia for you.

So this is how the heart normally works. In the next segment, you will be able to learn what goes amiss in your heart conduction. There is still tons of nursing information in our database. Aside from more EKG content, you can also drop by to check out on our wide variety of topics on anatomy and physiology, nursing fundamentals, and more.