Diastolic blood pressure is the pressure inside your arteries between heartbeats, when your heart is resting and refilling with blood. It’s the bottom number in a blood pressure reading. A normal diastolic pressure is below 80 mmHg, and readings of 90 mmHg or higher put you in the range of stage 2 hypertension.
What Happens Between Heartbeats
Your heart pumps in a cycle: squeeze, relax, squeeze, relax. The top number (systolic) captures the peak pressure when the heart contracts and pushes blood into the arteries. The bottom number (diastolic) captures the lowest pressure in that cycle, the moment just before the next contraction.
Even when the heart is relaxed, pressure in your arteries never drops to zero. Your large arteries are elastic, and they stretch when blood surges through during a heartbeat. Between beats, they recoil inward like a rubber band, maintaining enough force to keep blood flowing forward. That residual push is your diastolic pressure. In a healthy person, it sits around 80 mmHg in the body’s main circulation.
What the Numbers Mean
Under the 2025 guidelines from the American Heart Association and American College of Cardiology, diastolic blood pressure falls into these categories:
- Normal: below 80 mmHg
- Stage 1 hypertension: 80 to 89 mmHg
- Stage 2 hypertension: 90 mmHg or higher
- Hypertensive crisis: 120 mmHg or higher (with a systolic reading of 180 or above)
If your systolic and diastolic numbers fall into different categories, you’re classified by whichever one is higher. So a reading of 128/86 counts as stage 1 hypertension because of the diastolic number, even though 128 systolic alone would only be “elevated.”
How It’s Measured
When a clinician uses a traditional blood pressure cuff with a stethoscope, they listen for rhythmic tapping sounds in the artery as the cuff slowly deflates. The systolic reading is the pressure at which those sounds first appear. The diastolic reading is the pressure at which the sounds completely disappear. That moment of silence marks the point where blood is flowing freely through the artery even between heartbeats, and the cuff is no longer compressing it enough to cause turbulence.
Automatic home monitors use sensors to detect the same thing electronically. In either case, the bottom number on the display is your diastolic pressure.
Why Diastolic Pressure Matters for Your Heart
Your heart muscle gets most of its own blood supply between beats, not during them. When the heart contracts, it squeezes its own blood vessels shut. During the relaxation phase, diastolic pressure in the aorta is what drives blood into the small arteries feeding the heart muscle itself. If diastolic pressure is too low, less blood and oxygen reach the heart. Severe or prolonged drops can starve the heart muscle of oxygen, a condition that can lead to damage and, in extreme cases, a heart attack.
This is one reason doctors pay attention when diastolic pressure dips unusually low, especially in people who already have narrowed coronary arteries or heart failure. There’s a floor below which diastolic pressure stops being “good” and starts being risky.
High Diastolic Pressure in Younger Adults
Having a high diastolic number while your systolic number stays normal is called isolated diastolic hypertension. It’s more common in younger people. In a large study of middle-aged and older adults, about 11% of participants had this pattern.
Age changes the risk picture dramatically. Among adults aged 20 to 39, stage 1 isolated diastolic hypertension raised the risk of cardiovascular events by about 32%, and stage 2 raised it by 82%, compared to people with normal blood pressure. A separate study using 24-hour ambulatory monitoring found that in people under 50, isolated diastolic hypertension nearly tripled the risk of cardiovascular events. But in people over 50, that same pattern carried no statistically significant extra risk.
The takeaway: if you’re under 50 and your bottom number consistently runs in the 80s or 90s, it’s worth addressing even if the top number looks fine.
How Diastolic Pressure Changes With Age
Systolic and diastolic pressure don’t age the same way. Systolic pressure tends to climb steadily as you get older, driven by stiffening arteries. Diastolic pressure, on the other hand, typically rises until about age 50 and then starts to decline.
The reason comes back to arterial elasticity. Young, flexible arteries stretch when the heart pumps and snap back between beats, maintaining diastolic pressure. As arteries stiffen with age, they still get pushed outward by each heartbeat (raising systolic pressure), but they lose the ability to spring back effectively. That weakened recoil means less residual pressure between beats, so diastolic pressure drops. This is why many older adults develop a wide gap between their two numbers, something called a “wide pulse pressure,” which carries its own set of cardiovascular risks.
Lowering High Diastolic Pressure
The lifestyle changes that lower blood pressure in general work on diastolic pressure too, and the effects are surprisingly substantial when combined.
Regular aerobic exercise, things like brisk walking, cycling, swimming, or dancing for at least 30 minutes a day, can lower blood pressure by about 5 to 8 mmHg. Strength training twice a week adds further benefit. You don’t need to run marathons; consistency matters more than intensity, though high-intensity interval training also shows good results.
Diet has an even larger effect. A pattern rich in whole grains, fruits, vegetables, and low-fat dairy while cutting back on saturated fat can lower blood pressure by up to 11 mmHg. The DASH diet and Mediterranean diet are both built around this approach. Getting enough potassium (3,500 to 5,000 mg per day from foods like bananas, potatoes, and leafy greens) can lower pressure by another 4 to 5 mmHg. Reducing sodium to 1,500 mg per day, roughly half of what most people eat, drops it by an additional 5 to 6 mmHg.
Stack these together and you’re looking at reductions that rival what a single medication can achieve. For someone with a diastolic reading in the mid-80s, these changes alone may be enough to bring it back below 80.