Your blood pressure is the force inside your blood vessels when your heart beats and relaxes. This force is measured in millimeters of mercury (mm Hg).

The upper number — called your systolic pressure — is measured when your heart beats. The lower number — called your diastolic pressure — is measure when your heart relaxes between beats.

Most people worry about high blood pressure, which can increase your risk for heart disease or stroke, but low blood pressure can also be a problem.

The medical term for low blood pressure is hypotension. If you have hypotension, your systolic pressure measurement is under 90 mm Hg and your diastolic number is under 60 mm Hg.

In the last 10 to 15 years, doctors have started to be more concerned specifically about diastolic blood pressure below 60.

Some people can have low diastolic pressure even when their systolic pressure is normal. This condition is called isolated diastolic hypotension. Low diastolic blood pressure may be particularly dangerous for your heart.

Unlike the rest of your body, which receives blood when your heart pumps, the muscles of your heart receive blood when your heart relaxes. If your diastolic blood pressure is too low, your heart muscles won’t get enough oxygenated blood. This can lead to weakening of you heart, a condition called diastolic heart failure.

You may be at higher risk for this type of heart failure if you have coronary heart disease, which is narrowing of your heart arteries.

Symptoms of isolated diastolic hypotension include tiredness, dizziness, and falls.

Because low diastolic pressure decreases blood flow to your heart, you may also have chest pain (angina) or symptoms of heart failure. Heart failure symptoms may include shortness of breath, swelling of your feet or ankles, confusion, and heart palpitations.

Seek immediate medical attention if you have chest pain or difficulty breathing.

Symptoms of low diastolic blood pressure along with low systolic blood pressure (hypotension) include:

  • dizziness
  • fainting (syncope)
  • frequent falls
  • tiredness
  • nausea
  • blurred vision

Seek medical attention if you have any of these symptoms.

There are three known causes of isolated diastolic hypotension:

  • Alpha-blocker medications. These blood pressure medications work by causing your blood vessels to open up (dilate). Because they lower diastolic pressure more than systolic pressure, they may cause isolated diastolic hypotension. Common brand names include Minipress and Cardura.
  • The aging process. As we age, we lose the elasticity of our arteries. For some older adults, arteries may become too stiff to spring back between heartbeats, causing diastolic blood pressure to be low.
  • Too much salt in your diet. Dietary salt can decrease elasticity of your blood vessels. If you take in too much salt, you may increase your risk for low diastolic blood pressure.

There are several common causes of overall hypotension, which would include a low diastolic number.

  • Overtreatment of high blood pressure. For some people, especially people over age 60, lowering systolic blood pressure below 120 may cause diastolic pressure to fall below 60.
  • Other medications. Many medications besides those for blood pressure can cause hypotension. They include water pills (diuretics), Parkinson’s disease medications, antidepressants, and drugs used to treat erectile dysfunction.
  • Heart problems. Heart valve problems, heart failure, and a very slow heart rate (bradycardia) can lead to hypotension.
  • Dehydration. If you don’t take in enough fluids, your blood pressure can fall dangerously low. This may happen if you’re taking a diuretic and you lose more fluids than you take in.

Treating isolated diastolic hypotension is more difficult than treating general hypotension. If you’re taking an alpha-blocker, your doctor can change you to a different high blood pressure medication.

If you have isolated low diastolic pressure and you’re not on blood pressure medication, the only option may be to see your doctor more frequently for checkups and to watch for symptoms of heart failure. Currently, there isn’t any medication available to treat isolated diastolic hypotension.

Treatment of general hypotension depends on the cause.

Overtreatment of high blood pressure can be managed by adjusting or changing medications. The goal is to keep the diastolic blood pressure between 60 and 90 mm Hg. Your doctor may also change other medications that cause hypotension.

Dehydration can be treated with fluid replacement. In some cases, you may need medications that increase blood pressure.

There are some things you can do to help prevent and manage low diastolic pressure.

  • Try to keep your salt intake to between 1.5 and 4 grams per day. An ideal number is probably about 3.5 grams. You can do this by reading food labels and avoiding added salt in your diet.
  • Eat a heart-healthy diet. Eat plenty of fruits and vegetables, and include whole grains. For protein, stick to lean meats and fish. Avoid fatty foods.
  • Drink enough fluids and avoid alcohol, which can increase your risk for dehydration.
  • Stay physically active and start an exercise program. Ask your doctor what type and amount of exercise is safe for you.
  • Maintain a healthy weight. If you’re overweight, ask your doctor to help you with a safe weight loss plan.
  • Don’t smoke.

Hypotension can be dangerous because it’s a frequent cause of falls. Isolated diastolic hypotension can be especially dangerous because it can decrease blood flow to your heart.

You may be at higher risk if you have coronary artery disease. Over time, isolated diastolic hypotension can cause heart failure. In fact, it may be one of the most common causes of heart failure.

Pay attention to your diastolic number when you have your blood pressure checked. If your lower number is 60 or below, ask your doctor about it.

Let your doctor know if you have any symptoms of hypotension or heart failure. In many cases, switching medications along with making lifestyle changes can help. Your doctor may want to follow you more closely to ensure your diastolic pressure stays above 60.