My blood pressure lately has been around 140/75/64. Which is the most important reading? 140 seems high if normal is 120/80.

Pulse as without any, you wouldn't worry about any other stats.

Looks pretty normal though, depending on your age, stress level at time of measurement, and phase of the moon, take a number of readings over time and see if things change significantly.

Disclaimer: I'm not a doctor.

140/75 is borderline high. If this reading was taken at a hospital or doctor's office though, recheck it at home, several days in a row. The tension of being at the doctor's could be enough to explain a mild elevation.

If you are genuinely running in this range, reduce your sodium intake and, if at all overweight, loose weight. those two measures will likely do the trick in your case.

The top number -- systolic -- is very sensitive to transitory effects like pain, nervousness, etc. While the bottom number is much slower to change.

An occasional rise in systolic pressure coupkles with a normal diastolic is not a problem. but if your systolic is consistently around 140, or even 135, then some lifestyle modifications are in order.

Diastolic pressure represents the "minimum" pressure level that your vascular system is exposed to being the actual pressure when the heart relaxes. Chronic elevation here will lead to changes in the blood vessels and kidneys. This is the most reliable indicator of underlying or developing hypertension.

Systolic pressures go up with nervousness, stress, caffeine etc on a temporary basis but chronic elevation can lead to changes in the blood vessels which may make this a permanent change in the BP and the requires treatment.

Where systolic pressures are constantly about double the diastolic pressures, heart vale lesions such as a leaking aortic valve need to be ruled out as well as underlying metabilic diseases such as hyperthyroidism etc.

The level at which your pressures are (140/75), the "white coat" effect could be the culprit.

Best to take the BP in supine, sitting and standing positions and in both arms. Taken with a reliable BP machine, not one of these digital wrist monitors.