Heart failure is a medical condition that affects your heart’s ability to pump blood as it should. The condition is typically progressive, meaning that it gets worse over time. Your body usually tries to compensate in different ways.

In particular, heart failure can affect your preload and afterload — aspects of how much blood your heart puts out.

Let’s take a closer look at preload and afterload, as well as how heart failure affects these measurements.

Your heart is a pump that fills and refills to send out oxygen-rich blood to your vital organs. Preload and afterload can tell a doctor how well your heart performs these functions.

What is preload?

Your heart has two phases: systole and diastole. Systole is when your heart sends blood out, while diastole is when your heart refills with blood. If your heart doesn’t refill well, it won’t have enough blood to send out.

This is where preload comes in. Preload is the amount of “stretch” your heart has at its most full, right before it empties. This is why another name for preload is left ventricular end-diastolic pressure.

Preload requires enough blood and fluid to fill your heart, but it also requires your heart to be stretchy enough to fill up. If your heart is unhealthy, it may lack the ability to stretch to fill well.

What is afterload?

Afterload represents the next step in your heart’s cycle. Afterload is the pressure your heart has to overcome to eject the blood. Another name for afterload is systemic vascular resistance (SVR).

Your heart needs extra pressure to open the aortic valve to send blood out. It also relies on the balance of pressure in your veins. If your veins are too constricted (tight) or too high-pressured, blood will not flow as well. As a result, your heart will have to increase the pressure it uses to squeeze out blood.

What is contractility?

Contractility is the final piece of the puzzle related to preload and afterload. It refers to your heart’s ability to squeeze, regardless of what has filled it. Your contractility will be harmed if your heart becomes damaged, as it does with heart failure.

The amount of blood your heart can send out depends on these three variables: preload, afterload, and contractility.

Heart failure can affect your preload and afterload in different ways. Not every person with heart failure will experience these effects.

According to 2017 research, the following are the most common changes to preload and afterload, depending on your heart failure type.

Heart failure with reduced ejection fraction

The term “ejection fraction” refers to how much blood your heart sends out. Heart failure with reduced ejection fraction (HFrEF) occurs when your heart’s ejection fraction decreases to less than 40%. You’ll also experience changes to your heart’s appearance, such as its walls getting thicker.

Most people with HFrEF will experience decreases in contractility and increases in afterload.

Heart failure with preserved ejection fraction

In heart failure with preserved ejection fraction (HFpEF), your heart doesn’t fill up with enough blood. So even though it pumps out a regular percentage of blood, it’s still not enough to meet your body’s demands.

In HFpEF, preload will typically decrease because your heart isn’t able to relax as well as it should. Your afterload will also increase, often in an attempt to increase your blood pressure by tightening your blood vessels.

Right ventricular systolic dysfunction

Heart failure most commonly affects the left side of the heart first. However, some people’s left heart failure can ultimately lead to right heart failure as the heart tries to make up for the left side not working as well.

In right ventricular systolic dysfunction, a person will usually have decreased preload. This is because the right side of the heart isn’t working well and can’t fill the ventricle as well. They will also experience an increase in right ventricular afterload and decreases in contractility.

Changes to the heart, body fluid volume, and blood vessels can lead to changes in preload and afterload.

Factors that affect preload

Preload can increase or decrease. According to 2021 research, factors that increase preload include:

  • mitral regurgitation
  • aortic regurgitation
  • reduced heart rate (more time for the heart to fill)
  • reduced venous compliance (causes more blood to return to the heart from the veins)

Factors that decrease preload include:

  • mitral stenosis
  • hypovolemic shock
  • increased heart rate (less time for the heart to fill)
  • severe blood loss (hemorrhage)
  • severe nausea and vomiting that leads to dehydration

Factors that affect afterload

Afterload can also increase or decrease. Factors that can cause afterload to increase include:

Factors that can decrease afterload include medications prescribed to promote vasodilation and lower blood pressure. Examples of these medications include:

When you have heart failure, a doctor may prescribe medications that can affect your heart’s preload and afterload to improve how well your heart works.

It isn’t usually possible to reverse the effects of heart failure once they have occurred. But medications can help your heart perform as well as possible.

A doctor may prescribe medications that decrease preload to treat heart failure. While this may seem like an unusual approach, decreasing preload helps to reduce the amount of blood the heart has to pump. Reducing preload gives the heart a more reasonable workload.

Medications that decrease preload include:

You may notice many of these medications may also reduce afterload. By reducing afterload, these medications also decrease the heart’s work. The heart doesn’t have to generate as much pressure to send blood to your body’s organs.

A doctor may use a combination of these medications to treat heart failure. The doctor will frequently monitor your heart’s function to determine how well it’s working.

Heart failure can cause changes in your heart’s preload and afterload.

A doctor will commonly prescribe medications that affect each of these factors. These medications can reduce the effects of heart failure and ideally keep heart failure from getting worse.

Talk with your doctor to learn more about how your specific type of heart failure may affect preload and afterload and what medications can help.