Originally Posted by en bloc

Actually, the heart naturally increases if the BP drops...it is called a compensatory reaction, or in other words it compensates for the low BP. When your BP drops, the body automatically knows it needs more blood to get to the brain, so the heart rate picks up and goes much faster. So many people with NMH or OH have tachycardia when they stand...simply because their BP drops too low and the heart must compensate for the drop. However, POTS is when this increase in heart rate occurs WITHOUT any drop in BP. Two separate conditions...one where heart rate increases all by itself when they stand, and the other where it increases because the BP drops when they stand.

There are several names for BP dropping when standing...NMH and orthostatic hypotension are the most commonly ones used.