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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