Diastole vs. Systole: Know Your Blood Pressure Numbers

Medically Reviewed by Jabeen Begum, MD on March 03, 2023
8 min read

When you get your blood pressure numbers, there are two of them. The first, or “top” one, is your systolic blood pressure. The second, or “bottom,” one is diastolic blood pressure.

Knowing both is important and could save your life.

When your heart beats, it squeezes and pushes blood through your arteries to the rest of your body. This force creates pressure on those blood vessels, and that's your systolic blood pressure.

Here’s how to understand your systolic blood pressure number:

  • Normal: Below 120
  • Elevated: 120-129
  • Stage I: high blood pressure (also called hypertension): 130-139
  • Stage II: hypertension: 140 or more
  • Hypertensive crisis: 180 or more. Call 911.


The diastolic reading, or the bottom number, is the pressure in the arteries when the heart rests between beats. This is the time when the heart fills with blood and gets oxygen.

This is what your diastolic blood pressure number means:

  • Normal: Lower than 80
  • Stage I: hypertension: 80-89
  • Stage II: hypertension: 90 or more
  • Hypertensive crisis: 120 or more. Call 911.

Our chart below has more details.

Even if your diastolic number is normal (lower than 80), you can have elevated blood pressure if the systolic reading is 120-129.

If you have normal blood pressure, your blood pressure is less than 120/80. Stick with an active lifestyle and healthy diet to keep that going.

Is your blood pressure above the normal range, in either or both systolic and diastolic levels? Your doctor will want to have more than one blood pressure reading before diagnosing hypertension.

Treatments include lifestyle changes, and if that’s not enough, they may also include medications.

Lifestyle changes include:

  • Cutting back on sodium. Ask your doctor what your daily sodium limit should be. Read the Nutrition Facts label on food products.
  • Getting more exercise. Studies show benefits with 3-4 sessions per week, each lasting 40 minutes, of aerobic exercise (the kind that makes your heart beat faster).
  • Losing weight, if you’re overweight. You can expect to shave about 1 point off your blood pressure numbers for each pound lost.
  • Eating a healthy diet. The DASH diet is designed to improve blood pressure. DASH stands for Dietary Approaches to Stop Hypertension. It favors vegetables, fruits, whole grains, low-fat dairy, poultry, fish, and chicken.
  • Limiting alcohol to no more than one drink a day for women or two for men.

If you also need medication to lower your blood pressure, there are several types:

  • Diuretics
  • Angiotensin-converting enzyme inhibitors
  • Alpha blockers
  • Angiotensin II receptor blockers
  • Beta-blockers
  • Calcium channel blockers
  • Central agonists
  • Vasodilators
  • Combination medications

If you need medication, your doctor will consider which type is best for you. (They’ll also recommend lifestyle habits that help lower blood pressure.) Deciding whether you need medication is often done on a case-by-case basis, depending on what else is going on with your health and on your preferences.


If you have:

  • Elevated blood pressure: Your systolic pressure is 120-129, and your diastolic pressure is less than 80. Lifestyle changes and monitoring your blood pressure may be all you need at this point. Your doctor will let you know.
  • Stage I hypertension: Systolic 130-139 or diastolic 80-89. Your doctor will recommend lifestyle changes and will consider whether you also need medication.
  • Stage II hypertension: Systolic at least 140 or diastolic at least 90. Your doctor will recommend lifestyle changes and consider starting you on medication to lower your blood pressure.
  • Hypertensive crisis: Your blood pressure is 180/120 or higher. You may or may not also have symptoms such as chest pain, shortness of breath, numbness/weakness, and trouble with vision or with speaking. This is an emergency. Call 911.

One reading may not be enough to diagnose high blood pressure. Your doctor may want you to have several blood pressure readings over time, to check if it’s consistently too high.

A doctor or nurse will measure your blood pressure with a small gauge attached to an inflatable cuff. It's simple and painless.

The person taking your blood pressure wraps the cuff around your upper arm. Some cuffs go around the forearm or wrist, but often, they aren't as accurate.

Your doctor or nurse will use a stethoscope to listen to the blood moving through your artery.

They’ll inflate the cuff to a pressure higher than your systolic blood pressure, and it will tighten around your arm. Then, they’ll release it. As the cuff deflates, the first sound they hear through the stethoscope is the systolic blood pressure. It sounds like a whooshing noise. The point where this noise goes away marks the diastolic blood pressure.

In a blood pressure reading, the systolic number always comes first and then the diastolic number. For example, your numbers may be "120 over 80" or written as 120/80.


  • If your blood pressure is normalless than 120/80get it checked every year, or more often as your doctor suggests.
  • If your blood pressure is elevated—a systolic blood pressure between 120 and 129 or diastolic blood pressure of less than 80—your doctor will probably want to check it every 3-6 months. They will probably recommend lifestyle changes such as more exercise and a better diet.
  • If you have stage I hypertension—130-139 over 89-90—the doctor might suggest lifestyle changes and see you again in 3-6 months. They could also tell you to make the changes and give you medication, then recheck your condition in a month. It depends on what other health conditions or risk factors you have.
  • If you have stage II hypertension—140/90 or higher—you’ll likely get medication. You'll also need to make lifestyle changes and see the doctor again in a month.


Keeping track of blood pressure at home is important for many people, especially if you have high blood pressure. This helps you and your doctor find out if your treatment is working.

Your doctor may also suggest that you check your pressure at home if they think you may have "white coat hypertension." It's a real condition. The stress of being in a doctor's office increases your blood pressure, but when you're home, it's normal.

Ask your doctor to recommend an easy-to-use home blood pressure monitor. Make sure the cuff fits properly. If your arm is too big for the cuff, the reading may be higher than your blood pressure really is. Ask your doctor for a larger cuff or make sure you buy a home monitor with a cuff that fits you.

You also can use a wrist blood pressure monitor, but they often aren't as accurate. Follow the directions that come with the device to make sure you are using it correctly.

No matter which type of blood pressure monitor you have, it's a good idea to take it to your doctor's office. You can compare its reading to the numbers your doctor gets. Avoid caffeine, cigarettes, and exercise for at least 30 minutes before the test.

When you take your blood pressure at home, sit up straight in a chair and put both feet on the floor. Ask your doctor or nurse to show you the right way to position your arm so you get accurate readings.

Check it at the same time of day so the readings are consistent. Then, take several readings about 1 minute apart. Be sure to write down the results.

Take the blood pressure journal to your doctor's office so you can talk about any changes in your numbers. Your doctor will decide whether you need medications in addition to lifestyle changes.

Even if your blood pressure is high, you probably won't have symptoms. That's why it's often called the "silent killer." The first symptom of untreated high blood pressure may be a heart attack, stroke, or kidney damage.

To keep your blood pressure in the normal range, your daily habits are key. These things help:

Don’t smoke. Among the many health problems that smoking causes, it increases your blood pressure.

Make physical activity a habit. Most experts recommend at least 30 minutes of moderate-intensity physical activity (such as biking or brisk walking) five or more times a week. Or you could do a harder activity for a shorter period of time per session.

Eat right. Read food labels to see how much sodium is in a serving. Check with your doctor to find out what your daily limit should be. Include a lot of vegetables and fruits, along with whatever else you choose to put on your plate.

Stick to a healthy weight. Extra pounds increase your blood pressure. If you’re not sure what a healthy weight would be for you, ask your doctor.

Get enough sleep. For most adults, that’s 7-8 hours of sleep per night on a regular basis.

If you drink alcohol, limit it to no more than one drink a day if you’re a woman and up to two drinks a day if you’re a man.

Sometimes, your blood pressure will spike for short periods. This is known as sudden high blood pressure. Here are some of the causes:

  • Caffeine
  • Smoking
  • Stress
  • Certain medications such as nonsteroidal anti-inflammatory drugs or a mix of meds
  • Overactive adrenal glands
  • Chronic kidney disease
  • Thyroid issues (overactive or underactive thyroid)
  • Pregnancy-related high blood pressure


Malignant hypertension is extremely high blood pressure that develops rapidly and causes some type of organ damage. Malignant hypertension should be treated as a medical emergency.

In many people, high blood pressure is the main cause of malignant hypertension. Missing doses of blood pressure medications can also cause it. In addition, there are certain medical conditions that can cause it. They include:

  • Collagen vascular disease, such as scleroderma
  • Kidney disease
  • Spinal cord injuries
  • Tumor of the adrenal gland
  • Use of certain medications, including birth control pills and monoamine oxidase inhibitors
  • Use of illegal drugs, such as cocaine

Malignant hypertension is rare. About 1% of people who have a history of high blood pressure develop this life-threatening condition.

You are at higher risk of developing it if you are a man, African American, or someone of lower economic status. Poor access to health care increases the risk.

Malignant hypertension is a medical emergency and needs to be treated in a hospital, often in an intensive care unit. The doctor will consider your symptoms and overall health when deciding what treatment plan is best for you. The goal of treatment is to carefully lower your blood pressure within a matter of minutes.

You will receive blood pressure medicines through an IV, which is the quickest way to treat extremely high blood pressure. Once blood pressure is at a safe level, the medications may be switched to oral forms. If you develop kidney failure, you may need kidney dialysis.

Other treatments depend on your specific symptoms and possible causes of the malignant hypertension.