What the two numbers mean
Systolic pressure is the top number and reflects pressure when the heart contracts. Diastolic pressure is the bottom number and reflects pressure while the heart relaxes between beats.
Why one reading is not the whole story
Stress, pain, caffeine, talking, movement, and poor technique can change a reading. Trends from properly taken readings are usually more useful than a single isolated result.
When a reading is urgent
Very high readings paired with chest pain, shortness of breath, weakness, numbness, vision changes, or difficulty speaking can require emergency care.