Diastolic blood pressure is the second (bottom) number in a blood pressure reading, measuring the pressure in your arteries while the heart muscle rests between beats. According to current guidelines, a normal diastolic reading is less than 80 mm Hg, while elevated blood pressure is defined as a diastolic pressure of 80–89 mm Hg combined with a systolic pressure under 120 mm Hg.

High diastolic blood pressure (hypertension) is categorized into two stages:

• Stage 1 Hypertension: Diastolic pressure between 80 and 89 mm Hg.

• Stage 2 Hypertension: Diastolic pressure of 90 mm Hg or higher.

Low diastolic blood pressure is generally considered dangerous if it drops to 60 mm Hg or lower, which can be a sign of dehydration or severe bleeding, while 120 mm Hg or higher is alarmingly high.

Isolated Diastolic Hypertension occurs when the diastolic number is high (90 mm Hg or greater) while the systolic number remains 140 mm Hg or lower; this is most common in younger adults and is often associated with factors like obesity, smoking, and hormonal imbalances such as excess aldosterone. While the top (systolic) number is often prioritized for stroke and heart attack risk in older adults, the diastolic number remains a critical indicator of heart health, particularly for coronary vessels supplying oxygen to the heart muscle during rest.