Systolic vs. Diastolic: What the Numbers Mean

When you see a blood pressure reading like 120/80 mmHg, you’re looking at two distinct measurements:

• Systolic pressure (the top number): This measures the force your blood exerts against your artery walls when your heart contracts or beats. Think of it like the surge of water pressure in your home’s pipes when someone suddenly turns on a faucet. In our example, the systolic pressure is 120 mmHg.
• Diastolic pressure (the bottom number): This measures the force when your heart is at rest between beats. Continuing our plumbing analogy, this is like the baseline pressure that remains in your pipes even when no water is actively flowing. In our example, the diastolic pressure is 80 mmHg.

The unit “mmHg” stands for millimeters of mercury, which comes from the traditional way blood pressure was measured using a column of mercury that would rise and fall with each heartbeat.