Reviewed and updated by Lisa Bonsall, MSN, RN, CRNP, CCRN: February 13, 2024

A recent Quick Quiz on our Facebook page resulted in a mix of responses. Do you know what word is used to describe the amount of stretch on the myocardium at the end of diastole? The responses were split between cardiac preload and cardiac afterload. 
  Let’s take a closer look at what these terms mean.

Cardiac Preload

Preload, also known as the left ventricular end-diastolic pressure (LVEDP), is the amount of ventricular stretch at the end of diastole. Think of it as the heart loading up for the next big squeeze of the ventricles during systole. Some people remember this by using an analogy of a balloon – blow air into the balloon and it stretches; the more air you blow in, the greater the stretch. 

Cardiac Afterload

Afterload, also known as the systemic vascular resistance (SVR), is the amount of resistance the heart must overcome to open the aortic valve and push the blood volume out into the systemic circulation. If you think about the balloon analogy, afterload is represented by the knot at the end of the balloon. To get the air out, the balloon must work against that knot. 

Cardiac Output & Cardiac Index

Cardiac output is the volume of blood the heart pumps per minute. Cardiac output is calculated by multiplying the stroke volume by the heart rate; normal cardiac output is about 4 to 8 L/min but varies depending on the body’s metabolic needs. Cardiac index is a calculation of the cardiac output divided by the person’s body surface area (BSA). 

So, if you answered ‘D’ to the quiz above, you’re right!

Preload and Afterload References:

Hinkle, J., & Cheever, K. (2021). Brunner & Suddarth's Textbook of Medical-Surgical Nursing, Fifteenth edition. Philadelphia: Wolters Kluwer.

King, J., & Lowery, D. R. (2023). Physiology, Cardiac Output. In StatPearls. StatPearls Publishing.

Terzulli, D. (2023). A nurse's guide to hypovolemic shock. Nursing Made Incredibly Easy! 21(5). https://www.doi.org/ 10.1097/nme.0000000000000003 

 

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