When the heart pumps blood around the body its effectiveness is hindered by any plaque or clotting in the veins and arteries. Blood pressure rises when these veins and arteries are clogged. Blood pressure is affected by lack of exercise, age and diet.
Aerobic exercise several times a week is necessary to avoid the situation becoming dire. You can't necessarily feel or notice high blood pressure, but if you have it you're more likely to develop coronary heart disease or suffer a stroke. It's usual to be prescribed medication for lowering the blood pressure, and for this to be taken daily.