“SYS” on a blood pressure monitor stands for systolic pressure, the top number in a blood pressure reading. It measures the force your blood exerts against artery walls each time your heart beats and pushes blood out. A normal systolic reading is below 120 mmHg. Of the two numbers in a blood pressure reading, systolic pressure is the one most closely linked to heart disease and stroke risk, especially as you get older.
What Systolic Pressure Actually Measures
Every heartbeat has two phases. During the pumping phase, your heart’s lower chambers (ventricles) contract and force blood into your arteries. The pressure on your artery walls is at its highest during this moment, and that peak pressure is your systolic number. During the resting phase between beats, pressure drops to its lowest point. That lower number is your diastolic pressure, labeled “DIA” on most monitors.
So when your monitor reads SYS 118 and DIA 76, it means the force on your arteries peaks at 118 mmHg with each heartbeat and drops to 76 mmHg between beats. Together, this is written as 118/76.
What the Numbers Mean
The 2025 guidelines from the American Heart Association and American College of Cardiology classify blood pressure into four categories based on both numbers. If your systolic and diastolic fall into different categories, the higher category applies.
- Normal: Systolic below 120 and diastolic below 80
- Elevated: Systolic 120 to 129 and diastolic below 80
- Stage 1 hypertension: Systolic 130 to 139 or diastolic 80 to 89
- Stage 2 hypertension: Systolic 140 or higher or diastolic 90 or higher
On the low end, a systolic reading below 90 (paired with diastolic below 60) is generally considered low blood pressure. A sudden drop of just 20 points, say from 110 to 90, can cause dizziness or fainting. Persistent low readings with symptoms like blurred vision, lightheadedness, fatigue, or trouble concentrating are worth paying attention to.
Why the Top Number Matters More With Age
Most studies show a greater risk of cardiovascular disease, particularly stroke, related to high systolic pressure compared to elevated diastolic pressure. The reason comes down to what happens to your arteries over time.
As you age, your arteries gradually stiffen and lose their ability to stretch with each pulse of blood. Plaque buildup on artery walls accelerates this process, narrowing the vessels. Because the same volume of blood has to squeeze through stiffer, narrower passages, systolic pressure climbs while diastolic pressure stays the same or even drops. CDC data shows this pattern clearly: the average systolic reading is about 115 mmHg for adults 18 to 39, rises to 123 mmHg for ages 40 to 59, and reaches 136 mmHg for those 60 and older.
This is why some people, particularly older adults, develop a condition called isolated systolic hypertension. Their top number sits at 130 or above while the bottom number stays below 80. The high-pressure surges from each heartbeat damage the inner lining of arteries, which fuels more plaque buildup and further stiffening in a self-reinforcing cycle.
What Can Temporarily Spike Your SYS Reading
A single high reading doesn’t necessarily mean you have hypertension. Many everyday factors can push systolic pressure up temporarily:
- Stress and anxiety: Triggers a hormone surge that raises your heart rate and tightens blood vessels. This includes “white coat” anxiety from simply being in a clinic.
- Caffeine: Causes your body to release adrenaline, which narrows blood vessels and speeds up your heart.
- Dehydration: Reduces your blood volume, forcing your heart to pump harder.
- A full bladder: Puts pressure on your kidneys and can elevate readings.
- Pain: Triggers a stress response that temporarily raises pressure.
This is exactly why a hypertension diagnosis requires elevated readings at two separate visits, with at least two measurements taken each time. One high number on a stressful morning doesn’t tell the full story.
Getting an Accurate Reading at Home
If you’re monitoring at home, small details affect accuracy, particularly for the systolic number. The inflatable part of your cuff should wrap around 75% to 100% of your upper arm’s circumference. A cuff that’s too small will give falsely high readings, while one that’s too large will read low. Width matters too: the cuff should cover roughly 40% to 80% of the distance between your elbow and shoulder.
Take two readings each time, waiting about one minute between them, and use the average. Sit with your back supported, feet flat on the floor, and your arm resting at heart level. Avoid caffeine, exercise, and smoking for at least 30 minutes beforehand. Checking at the same time each day gives you the most consistent picture of where your systolic pressure typically sits.