---
title: "Diastolic Pressure | Intro to Pharmacology"
description: "Diastolic pressure is the lower blood pressure number, showing artery pressure between heartbeats and guiding how pharmacology evaluates hypertension treatment."
canonical: "https://fiveable.me/introduction-to-pharmacology/key-terms/diastolic-pressure"
type: "key-term"
subject: "Intro to Pharmacology"
unit: "Unit 7"
---

# Diastolic Pressure | Intro to Pharmacology

## Definition

Diastolic pressure is the lower number in a blood pressure reading, showing the pressure in the arteries when the heart relaxes between beats. In Intro to Pharmacology, it matters when you study hypertension and how antihypertensive drugs change vascular resistance and blood flow.

## What It Is

In Intro to Pharmacology, diastolic pressure is the arterial pressure measured during the heart’s relaxation phase, between contractions. It is the lower number in a blood pressure reading, such as 120/80 mmHg, where 80 is the diastolic pressure.

That lower number is not just a leftover from the reading. It reflects how much pressure is still in the arteries when the ventricles are filling with blood. If the vessels stay too constricted, diastolic pressure rises because blood keeps pushing against more resistance even while the heart is resting.

This is why diastolic pressure matters when you study antihypertensive drugs. Many blood pressure medications work by lowering peripheral vascular resistance, which can reduce the pressure in the arteries during relaxation. Calcium channel blockers and ARBs, for example, can help lower diastolic pressure by relaxing blood vessels and making it easier for blood to flow.

A common mix-up is treating blood pressure as one number. In pharmacology, you look at both systolic and diastolic pressure because they can point to different problems. A person can have a normal systolic number with an elevated diastolic number, especially if vascular tone is increased. That matters when a drug is chosen, adjusted, or evaluated for effect.

Clinically, normal diastolic pressure is often around 60 to 80 mmHg. Repeated readings above that range can suggest hypertension or poor blood vessel relaxation. So when you see diastolic pressure in a case study or practice problem, think about the state of the arteries, not just the heartbeat itself.

## Why It Matters

Diastolic pressure is one of the main numbers you use to judge whether an antihypertensive drug is doing its job. If a medication lowers blood pressure by relaxing vessels, reducing fluid volume, or slowing heart activity, the diastolic number often shifts along with the systolic number. That makes it a useful marker for treatment response, not just a random value on a vital signs chart.

It also helps you connect drug class to mechanism. For example, drugs that reduce vascular resistance can bring down diastolic pressure by making arteries less constricted. If you are looking at a case, the diastolic reading can hint at whether the patient’s high blood pressure is more about vessel tone than about heart rate alone.

This term also shows up in side effect discussions. A medication that lowers pressure too much can lead to dizziness, weakness, or orthostatic symptoms, especially when the patient stands up. So diastolic pressure is part of the safety picture, not just the diagnosis picture.

In short, this number helps you interpret blood pressure changes in a pharmacology setting and connect the reading to the drug’s mechanism, the patient’s symptoms, and the treatment goal.

## Connections

### [Systolic Pressure](/introduction-to-pharmacology/key-terms/systolic-pressure)

Systolic pressure is the upper number in a blood pressure reading, and it measures arterial pressure when the heart contracts. Together with diastolic pressure, it gives you the full picture of blood pressure control. In pharmacology, a drug may lower both numbers, but the pattern can tell you something about vascular resistance, cardiac output, and whether treatment is working as expected.

### [Hypertension](/introduction-to-pharmacology/key-terms/hypertension)

Hypertension is the condition diastolic pressure can help reveal when readings stay too high over time. In Intro to Pharmacology, you use blood pressure values to decide whether a patient may need treatment and to track whether a drug is lowering pressure enough. Elevated diastolic pressure can point to increased resistance in the arteries.

### [Calcium Channel Blockers](/introduction-to-pharmacology/key-terms/calcium-channel-blockers)

Calcium channel blockers lower blood pressure by relaxing blood vessels, which can reduce diastolic pressure. That connection makes them a common example when you study how antihypertensive drugs change vascular tone. If a case shows high pressure from constricted arteries, this drug class is a likely mechanism-based match.

### [Vasodilation](/introduction-to-pharmacology/key-terms/vasodilation)

Vasodilation means blood vessels widen, which lowers resistance to blood flow. When arteries dilate, diastolic pressure often drops because blood meets less pushback during the heart’s resting phase. Many antihypertensive drugs aim for this effect, so vasodilation is one of the clearest mechanisms tied to a lower diastolic reading.

## On the AP Exam

A quiz question may give you a blood pressure reading and ask which number is the diastolic pressure, or it may ask what an elevated diastolic value suggests. On problem sets and case studies, you might connect a high diastolic reading to increased vascular resistance or to the effect of a drug class like calcium channel blockers or ARBs. If the question shows a patient with dizziness after starting treatment, you may need to think about blood pressure being lowered too far, including the diastolic number. The main move is to read the number, identify what phase of the cardiac cycle it reflects, and connect that to the drug’s mechanism or the patient’s symptoms.

## Diastolic Pressure vs Systolic Pressure

These two are easy to mix up because they appear together in the same reading. Systolic pressure is the top number and reflects pressure during contraction, while diastolic pressure is the bottom number and reflects pressure during relaxation. In pharmacology questions, that difference matters because a drug may affect the numbers differently depending on whether it changes cardiac output or vascular resistance.

## Key Takeaways

- Diastolic pressure is the lower blood pressure number, and it shows arterial pressure when the heart relaxes between beats.
- In Intro to Pharmacology, diastolic pressure matters because antihypertensive drugs often change it by lowering vascular resistance or changing blood flow.
- A consistently elevated diastolic pressure can point to hypertension and may signal that blood vessels are too constricted.
- You always read diastolic pressure together with systolic pressure, since the pair gives a better picture of cardiovascular status than either number alone.
- If a treatment lowers blood pressure too much, the diastolic number can help you spot possible overcorrection or side effects like dizziness.

## FAQs

### What is diastolic pressure in Intro to Pharmacology?

Diastolic pressure is the lower number in a blood pressure reading and shows the pressure in the arteries when the heart is relaxing between beats. In pharmacology, it comes up when you study hypertension and how drugs change vascular resistance. It is one of the main numbers used to judge whether blood pressure treatment is working.

### Is diastolic pressure the top or bottom number?

It is the bottom number. The top number is systolic pressure, which reflects pressure during heart contraction, while diastolic pressure reflects pressure during relaxation. Knowing the difference helps you interpret drug effects and blood pressure cases correctly.

### Why does diastolic pressure matter for antihypertensive drugs?

Many antihypertensive drugs lower pressure by relaxing blood vessels, reducing fluid volume, or changing heart activity. Diastolic pressure shows how much resistance remains in the arteries during the heart’s resting phase, so it is a useful number for tracking treatment response. A falling diastolic reading can mean the drug is reducing vascular resistance.

### What does a high diastolic pressure mean?

A high diastolic pressure often suggests increased resistance in the arteries and can be a sign of hypertension. In pharmacology, that can help you connect the reading to the need for treatment or to a drug class that lowers vessel tone. It is not diagnosed from one number alone, but repeated high readings matter.

## Related Study Guides

- [7.1 Antihypertensive drugs](/introduction-to-pharmacology/unit-7/antihypertensive-drugs/study-guide/PQK28ba8Ro49LSVt)

## About This Document

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