---
title: "Ventricular Diastole | Anatomy and Physiology I"
description: "Ventricular diastole is the heart's relaxation and filling phase, when AV valves open and blood enters the ventricles in Anatomy and Physiology I."
canonical: "https://fiveable.me/anatomy-physiology/key-terms/ventricular-diastole"
type: "key-term"
subject: "Anatomy and Physiology I"
unit: "Unit 19"
---

# Ventricular Diastole | Anatomy and Physiology I

## Definition

Ventricular diastole is the relaxation phase of the ventricles in the cardiac cycle, when they fill with blood before the next contraction. In Anatomy and Physiology I, it is the setup phase that determines how much blood the heart can pump next.

## What It Is

Ventricular diastole is the part of the cardiac cycle when the ventricles relax and fill with blood. In Anatomy and Physiology I, this is the phase that follows ventricular systole, and it is what prepares the heart for the next round of pumping.

During diastole, ventricular pressure falls. Once the pressure inside the ventricles drops below atrial pressure, the atrioventricular valves, the tricuspid valve on the right and the mitral valve on the left, open and blood flows into the ventricles. That flow is driven by a pressure gradient, not by the ventricles actively squeezing.

The filling phase is not just one motion. Early diastolic filling happens quickly at first, then diastasis is a slower filling period, and atrial systole gives a final push of blood into the ventricles. That last push matters most when heart rate is high, because there is less time for passive filling.

By the end of ventricular diastole, the ventricles contain their maximum volume of blood for that beat. That volume is called end-diastolic volume, or EDV. EDV is a big reason diastole matters, because the more the ventricle fills, the more it can stretch before contraction, which affects the force of the next systole through the Frank-Starling relationship.

Diastole is also where the heart muscle gets a break. While the ventricles are relaxing, the coronary circulation can deliver oxygen and nutrients to the heart tissue itself. If diastole is too short, such as during a very fast heart rate, filling drops and coronary perfusion time also shrinks.

## Why It Matters

Ventricular diastole is the setup for the whole pumping cycle, so it connects directly to stroke volume, cardiac output, and blood pressure. If the ventricles do not fill well, they cannot eject as much blood on the next beat. That makes diastole a useful place to think about why heart rate, valve function, and ventricular compliance all change circulation.

It also gives you a clear way to read pressure changes in the cardiac cycle. When ventricular pressure falls below atrial pressure, the AV valves open. When the ventricles fill enough to raise pressure again, the valves close later in the cycle. That back-and-forth timing is one of the main patterns you track in heart diagrams, pressure graphs, and lab questions.

Diastole matters even more when you compare a healthy heart to a stiff or damaged one. A ventricle with poor compliance does not relax well, so it fills less efficiently. In class, that idea often shows up in questions about why a person can have normal contraction strength but still low filling and reduced output.

## Connections

### [Ventricular Systole](/anatomy-physiology/key-terms/ventricular-systole)

Ventricular systole is the contraction phase that follows ventricular diastole. Diastole fills the ventricles, and systole pumps that blood out into the pulmonary trunk and aorta. If you track the cardiac cycle step by step, these two phases alternate by changes in pressure and valve position.

### Preload

Preload is the amount of stretch in the ventricular walls before contraction, and it depends largely on how much blood enters during ventricular diastole. More filling usually means a larger preload, which can increase the force of the next contraction. That is why filling time matters so much in circulation problems.

### [Atrioventricular Valves](/anatomy-physiology/key-terms/atrioventricular-valves)

The tricuspid and mitral valves are open during ventricular diastole so blood can move from the atria into the ventricles. They close when ventricular pressure rises during systole to prevent backflow. If you are tracing the heart cycle, these valves are a good clue for deciding whether the ventricles are filling or ejecting.

### [End-Diastolic Volume](/anatomy-physiology/key-terms/end-diastolic-volume)

End-diastolic volume, or EDV, is the amount of blood in a ventricle at the end of diastole. It is the direct result of ventricular filling and is often used to describe how full the ventricle is before it contracts. EDV is a common number in cardiac output and stroke volume questions.

## On the AP Exam

A quiz question may ask you to identify what happens when the ventricles are relaxed, label a heart diagram, or predict valve status from pressure changes. You might also need to trace how a faster heart rate shortens filling time and lowers end-diastolic volume. In lab or class discussion, ventricular diastole often shows up when you compare pulse rate, stroke volume, or a cardiac cycle graph. If you see the ventricles relaxing, the AV valves open, and blood moving in from the atria, you are looking at diastole, not systole.

## Ventricular Diastole vs Ventricular Systole

These are opposite phases of the same cycle. Ventricular diastole is the relaxation and filling phase, while ventricular systole is the contraction and ejection phase. A common mix-up is thinking the heart fills while it squeezes, but filling happens when ventricular pressure is low and the chambers are relaxed.

## Key Takeaways

- Ventricular diastole is the relaxation phase when the ventricles fill with blood before the next heartbeat.
- During diastole, ventricular pressure drops and the atrioventricular valves open so blood can move from the atria into the ventricles.
- The amount of filling during diastole becomes end-diastolic volume, which affects the strength of the next contraction.
- Fast heart rates can shorten diastole, leaving less time for filling and reducing preload.
- If a ventricle is stiff or less compliant, it does not relax and fill as well during diastole.

## FAQs

### What is ventricular diastole in Anatomy and Physiology I?

It is the phase of the cardiac cycle when the ventricles relax and fill with blood. In this course, you usually connect it to valve opening, pressure changes, and the buildup of end-diastolic volume before the next contraction.

### What happens to the valves during ventricular diastole?

The atrioventricular valves, the tricuspid and mitral valves, are open so blood can flow from the atria into the ventricles. The semilunar valves are not the ones doing the main work in this phase because the heart is in its filling stage, not its ejection stage.

### How is ventricular diastole different from atrial systole?

Ventricular diastole is about the ventricles relaxing and filling, while atrial systole is the atria contracting to top off the ventricles. Atrial systole happens near the end of ventricular diastole, so they are connected, but they are not the same event.

### Why does ventricular diastole matter for cardiac output?

The more completely the ventricles fill, the more blood is available to eject during the next systole. If diastole is shortened, for example with a very fast heart rate, filling drops and stroke volume can fall too.

## Related Study Guides

- [19.3 Cardiac Cycle ](/anatomy-physiology/unit-19/3-cardiac-cycle/study-guide/YvRk8a3OeQm0aWtw)

## About This Document

Canonical Fiveable pages are available as Markdown at the same path plus `.md`.

- [llms.txt](https://fiveable.me/llms.txt): index of Fiveable's sections and URL patterns
- [llms-full.txt](https://fiveable.me/llms-full.txt): complete subject and unit listing
- [MCP server](https://fiveable.me/mcp): call Fiveable as tools instead of fetching pages (`https://fiveable.me/api/mcp`)
- [MCP server for AP teachers](https://fiveable.me/mcp/teachers): a teacher's classes, assignments and AP-rubric grading (`https://fiveable.me/api/mcp/teacher`)

## Structured Data

```json
{"@context":"https://schema.org","@graph":[{"@type":"LearningResource","@id":"https://fiveable.me/anatomy-physiology/key-terms/ventricular-diastole#resource","name":"Ventricular Diastole | Anatomy and Physiology I","url":"https://fiveable.me/anatomy-physiology/key-terms/ventricular-diastole","learningResourceType":"Concept explainer","educationalLevel":"AP® / High School","about":{"@id":"https://fiveable.me/anatomy-physiology/key-terms/ventricular-diastole#term"},"audience":{"@type":"EducationalAudience","educationalRole":"student"},"dateModified":"2026-07-03T02:20:43.193Z","isPartOf":{"@type":"Collection","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"},"author":{"@type":"Organization","@id":"https://fiveable.me/editorial#content-team","name":"Fiveable Content Team","url":"https://fiveable.me/editorial","parentOrganization":{"@id":"https://fiveable.me/#organization"},"member":[{"@type":"Person","name":"Amanda DoAmaral","sameAs":["https://www.linkedin.com/in/adoamaral"]},{"@type":"Person","name":"Becky Bahr","sameAs":["https://www.linkedin.com/in/becky-bahr-b52743132"]}]},"publisher":{"@type":"Organization","name":"Fiveable","url":"https://fiveable.me"}},{"@type":"DefinedTerm","@id":"https://fiveable.me/anatomy-physiology/key-terms/ventricular-diastole#term","name":"Ventricular Diastole","description":"Ventricular diastole is the relaxation phase of the ventricles in the cardiac cycle, when they fill with blood before the next contraction. In Anatomy and Physiology I, it is the setup phase that determines how much blood the heart can pump next.","url":"https://fiveable.me/anatomy-physiology/key-terms/ventricular-diastole","inDefinedTermSet":{"@type":"DefinedTermSet","name":"Anatomy and Physiology I Key Terms","url":"https://fiveable.me/anatomy-physiology/key-terms"}},{"@type":"FAQPage","mainEntity":[{"@type":"Question","name":"What is ventricular diastole in Anatomy and Physiology I?","acceptedAnswer":{"@type":"Answer","text":"It is the phase of the cardiac cycle when the ventricles relax and fill with blood. In this course, you usually connect it to valve opening, pressure changes, and the buildup of end-diastolic volume before the next contraction."}},{"@type":"Question","name":"What happens to the valves during ventricular diastole?","acceptedAnswer":{"@type":"Answer","text":"The atrioventricular valves, the tricuspid and mitral valves, are open so blood can flow from the atria into the ventricles. The semilunar valves are not the ones doing the main work in this phase because the heart is in its filling stage, not its ejection stage."}},{"@type":"Question","name":"How is ventricular diastole different from atrial systole?","acceptedAnswer":{"@type":"Answer","text":"Ventricular diastole is about the ventricles relaxing and filling, while atrial systole is the atria contracting to top off the ventricles. Atrial systole happens near the end of ventricular diastole, so they are connected, but they are not the same event."}},{"@type":"Question","name":"Why does ventricular diastole matter for cardiac output?","acceptedAnswer":{"@type":"Answer","text":"The more completely the ventricles fill, the more blood is available to eject during the next systole. If diastole is shortened, for example with a very fast heart rate, filling drops and stroke volume can fall too."}}]},{"@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"name":"Anatomy and Physiology I","item":"https://fiveable.me/anatomy-physiology"},{"@type":"ListItem","position":2,"name":"Key Terms","item":"https://fiveable.me/anatomy-physiology/key-terms"},{"@type":"ListItem","position":3,"name":"Unit 19","item":"https://fiveable.me/anatomy-physiology/unit-19"},{"@type":"ListItem","position":4,"name":"Ventricular Diastole"}]}]}
```