As a result, this evaporative cooling mechanism becomes ineffective and inefficient. In an effort to compensate, the peripheral arteries near the skin dilate, so that greater amounts of blood can be transferred to the skin's surface. This compensory process is responsible for the characteristic "flushed look" individuals have when they become overheated. Redirecting blood flow to the peripheral arteries requires the heart to work harder. In fact, the heat stress associated with using a sauna, hot tub or steam room can be enough to cause the heart rate of a hypertensive individual to nearly double in fewer than 10 minutes. In addition to performing its usual task of supplying the muscles and other vital organs (e.g., the brain) with sufficient amounts of blood, oxygen and nutrients, the heart struggles to meet the demands for increased blood flow to the dilated peripheral arteries. The dilation of the peripheral arteries results in significantly less resistance to blood flow and, concomitantly, a dramatic drop in blood pressure (clinically referred to as hypotension).

Research has shown that heat stress from saunas, hot tubs and steam rooms typically won't cause significant blood pressure changes in normotensive individuals. Hypertensive individuals on medication, however, may experience a rather sudden, dramatic drop in blood pressure. Such a hypotensive response can result in symptoms such as dizziness, lightheadedness and fainting. In order to compensate, the heart beats more rapidly, attempting to supply blood to all areas of the body that require it.