The heart pumps blood into the circulatory system. If the pressure in the circulatory system is higher than it should be, then the heart has to work harder. Since the heart is composed of muscle, this extra “work” causes the heart muscle to get bigger, just like lifting weights makes arm and leg muscles get bigger. However, what’s good for arms and legs may not be good for the heart.

Although both the right and left ventricle of the heart pump blood, the left ventricle is the real “workhorse.” The right ventricle of the heart pumps blood to the lungs, which is a relatively low-pressure system. The left ventricle, however, has to pump blood to the rest of the body. This pumping action naturally requires a higher pressure. In people with hypertension, the left ventricle has to pump against an even higher pressure.

Over a period of time, the left ventricle becomes thicker and more muscular as a result of the extra work. This increased thickness of the ventricular wall is due to an increased number of heart muscle cells, an increase in the size of the cells, and an increase in the fibrous material that holds them together. This condition is called left ventricular hypertrophy (LVH) and can sometimes be seen on an electrocardiogram or during an echocardiogram.

LVH develops initially as a protective response, designed to make sure that the heart pumps out enough blood to all the organs of the body despite the higher baseline pressure in the circulatory system it must overcome. Eventually, however, the increased thickness of the heart’s walls interferes with proper function. A ventricular wall that is thick and muscular is stiff and doesn’t expand easily. This causes a reduced volume in the chamber and smaller amounts of blood pumped out to the body. If high blood pressure goes untreated, this condition may lead to heart failure.