(1) Heart failure. -In severe heart failure the arteries and arterioles
may be more constricted than they need be, increasing the work load on the
heart. Arterial vasodilators can then help by directly reducing the resistance
against which the heart has to pump. Venous vasodilators (venodilators) help
the veins carry an increased volume of blood and so may relieve shortness of
breath.
(2) High blood pressure. -High blood pressure is due to an
inappropriately high resistance in the arterioles and arterial vasodilators reduce this directly. They are generally used in combination with other
antihypertensive drugs, such as diuretics of “beta-blockers.”
(3) Angina. -Angina is the pain which signals that some portion of the
heart cannot get enough blood through the coronary arteries. When the heart
works harder (during exercise or stress) the flow of blood through the
coronary arteries normally increases. This may not be possible if a coronary
artery is narrowed by a fatty deposit. It may still be possible to dilate such
coronary arteries at their critically narrowed point by a vasodilator drug.
Vasodilators also help by reducing the resistance against which the heart has
to beat so that the work load on the heart and thus its energy needs are
slightly reduced.