The Difference Between Systolic and Diastolic Blood Pressures

By Andrew Yocum, MD
Medically reviewed checkmarkMedically reviewed
April 15, 2022

Blood pressure is one of the vital signs used to check how well your body is working.

High blood pressure, or hypertension, can increase the risk of heart disease and stroke, yet it often doesn’t cause any symptoms. Instead, the only way you know your blood pressure is elevated is to get a blood pressure reading.

You may have noticed that blood pressure is measured using two numbers, with one “over” the other.

Both numbers are important, and each can also tell you something about your health on its own.

In this article, I’ll explain blood pressure and the differences between systolic and diastolic blood pressure.

I’ll also discuss ways to prevent high blood pressure and when to see a doctor about your blood pressure. 

What Is Blood Pressure?

The heart supplies the body with oxygen and nutrients by constantly pumping blood through blood vessels called arteries.

Blood pressure is the force blood puts on the arteries as it flows through them.

It is measured in units of millimeters of mercury (mmHg).  

The size and flexibility of the arteries affect blood pressure.

If the arteries are stiff and narrow, blood will put more pressure on the artery walls, resulting in higher blood pressure.

With more relaxed arteries, there is less resistance to blood flow, leading to lower blood pressure. 

Hypertensive 

Doctors diagnose hypertension when a patient’s blood pressure is consistently 130/80 mmHg or higher. 

A hypertensive person experiences greater resistance to blood flow in the arteries, so their heart has to work harder to transport blood throughout the body.

This increases the risk for other serious health problems such as stroke, heart attack, and heart failure. 

Hypotensive 

A person is hypotensive when their blood pressure is much lower than normal, typically 90/60 mmHg or lower.

In this case, the heart doesn’t push blood through the arteries with enough force. 

For some people, being hypotensive is normal and causes no problems.

For others, low blood pressure may mean some organs get insufficient blood. 

Severe hypotension can be caused by a heart attack, sudden blood loss, and severe infection.

Hypotension can also be caused by dehydration or certain medicines, including diuretics, anti-anxiety medication, and some antidepressants.

Talk to your healthcare provider if you are concerned that you may have hypotension.

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Systolic vs. Diastolic Blood Pressure

Blood pressure is typically recorded as one number “over” another.

The first or top number is systolic blood pressure. The second or bottom number is diastolic blood pressure.

Systolic pressure measures the force of the blood against the artery walls when the heart beats (squeezes).

Diastolic blood pressure measures the force when the heart rests between beats.  

Both numbers are important in monitoring heart health.

However, studies have shown that, compared to elevated diastolic blood pressure, high systolic blood pressure is associated with a greater risk of stroke and heart disease.

High systolic blood pressure is also a stronger indicator of the risk of death compared to high diastolic pressure. Because of all of this, doctors tend to monitor systolic pressure more closely, especially in older patients.

Some people have very high systolic blood pressure (above 140 mmHg) and normal diastolic blood pressure (below 90 mmHg), or isolated systolic hypertension.

People with ISH also have higher pulse pressure, which is the difference between systolic and diastolic pressure. ISH can increase the risk of cardiovascular disease and stroke. 

How to read blood pressure

Your healthcare provider can take your blood pressure readings.

You can also read your blood pressure at home using a blood pressure monitor.

Follow your provider’s directions or the guidelines below for the most accurate readings:

  • Rest: Blood pressure rises naturally after physical activity, so avoid taking a reading within 30 minutes of any type of exertion. 
  • Sit correctly: Sit with your back straight, feet flat on the floor, and legs uncrossed. Then support the arm that you’re using for the measurement  on a flat surface (like a table) with your upper arm at heart level. 
  • Place the cuff correctly: Check the instructions of your monitor for precise directions. In general, place the bottom of the blood pressure cuff directly on your skin (rather than over clothing) above the bend of your elbow. 
  • Take multiple readings: Each time you measure your blood pressure, take 2-3 readings one minute apart from each other. Do this twice daily at the same times each day.

A single high BP reading does not mean you’re hypertensive.

If you get a reading that’s high for you, rest for a few minutes, then take a few more blood pressure readings. If those are high, contact your healthcare provider. 

Blood pressure ranges

What is normal range blood pressure varies some from person to person.

In general, healthcare providers use the ranges below to categorize blood pressure:

CategorySystolic Blood PressureDiastolic Blood Pressure
Low blood pressureLess than 90 mmHgLess than 60 mmHg
Normal blood pressureLess than 120 mmHgLess than 80 mmHg
Elevated blood pressure120-129 mmHgLess than 80 mmHg
High blood pressure (stage 1)130-139 mmHg80-89 mmHg
High blood pressure (stage 2)140+ mmHg90+ mmHg
Hypertensive crisisHigher than 180 mmHgHigher than 120 mmHg

Consult your doctor if you have any unusually high or low readings.

Seek immediate attention if you have hypertensive crisis-range readings. 

Preventing High Blood Pressure

High blood pressure puts you at risk for many heart-related conditions.

Luckily, even if hypertension runs in your family, lifestyle changes can help prevent or lower high blood pressure:

If lifestyle changes are not enough to lower high blood pressure, your doctor may recommend blood pressure medication

Concerned about blood pressure? Chat with a provider using K Health.
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When to See a Doctor

If you monitor your blood pressure at home, see your doctor if you consistently have high blood pressure readings or if your systolic blood pressure is unusually high. 

However, call 911 or go to the emergency room if your blood pressure reads 180/120 mmHg or higher.

Such a high reading is considered a hypertensive crisis and requires immediate medical attention.

How K Health Can Help

Did you know you can get affordable primary care with the K Health app? Download K to check your symptoms, explore conditions and treatments, and if needed, text with a doctor in minutes. K Health’s AI-powered app is HIPAA compliant and based on 20 years of clinical data.

Frequently Asked Questions

Is systolic or diastolic more important in blood pressure readings?
Both systolic and diastolic blood pressure are important. However, having a higher systolic reading has more health implications.
What is the difference between systolic or diastolic heart failure?
Systolic heart failure occurs when the heart muscle loses its ability to contract properly and therefore can’t pump forcefully enough to move blood around the body. Systolic heart failure is also known as heart failure with reduced ejection fraction (HFrEF). In diastolic heart failure, although the heart is strong enough to pump properly, it can’t fill up with blood because the heart muscle is stiff. In this case, the amount of blood pumped out to the body is reduced. Diastolic heart failure is also called heart failure with a preserved ejection fraction (HFpEF).
How can you read your own blood pressure at home?
You can measure your blood pressure using a blood pressure monitor.
K Health articles are all written and reviewed by MDs, PhDs, NPs, or PharmDs and are for informational purposes only. This information does not constitute and should not be relied on for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment.

Andrew Yocum, MD

Dr Andrew Yocum is a board certified emergency physician. He graduated Summa Cum Laude from Kent State University with a Bachelor of Science in Molecular Biology before attending Northeast Ohio Medical University where he would earn his Medical Doctorate (MD).