Hypertension, or high blood pressure, is one of the major causes of heart failure. If this condition shown below is left unchecked, it can ultimately damage the heart.

The diagram demonstrates the effect that a change in vessel diameter can induce to blood flow. As vessel diameters grow smaller and smaller, the result is not unlike what occurs to water flow out of a hose when a small kink is placed in it. In order for it to bypass this increased resistance to flow, it must be pushed with a greater pressure or force. In much the same way, an increase in the body's blood vessel resistance to flow places a new burden upon the heart to push blood through the smaller opening. It is largely unknown why the body chooses to raise resistance to flow even after it becomes a chronic burden on the heart.

Another factor that can contribute to high blood pressure is a large blood volume, generally caused by salt and water intake exceeding the rate of excretion by the kidneys. If kidneys receive a reduced blood flow for any reason, this will limit the amount of water excreted.