KB-C is a Chinese formula, so it addresses the body as a whole, not just one specific problem. My experience with the Chinese formulas is that they often exert a "balancing" effect upon the body. In support of this, the formula contains the adaptogens Astragalus and Panax ginseng (Korean ginseng). KB-C will help reduce high blood pressure, due to the herbs' abilities for increasing circulation, dilating constricted blood vessels, strengthening heart function, promoting diuretic activity where there is fluid retention, and providing an overall tonic effect on the body. However, this formula may also help to normalize low pressure, since many of these same herbs help strengthen heart function, as well as provide a toning/building effect upon the body.
For more information on KB-C, see the HART Toolkit or HART on CD.