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Vascular effects of diuretics in heart failure.

Diuretics have been the standard treatment for heart failure for several decades. The primary action is renal in promoting diuresis, but diuretics also alter vascular conductance and this may enhance their efficacy in heart failure.' The syndrome of chronic heart failure is associated with changes in vascular conductance peripherally and it is appropriate to summarise those changes before reviewing the vascular effects of diuretics.2' Patients with chronic heart failure, who are stabilised on treatment, are encouraged to exercise as part of modern management.4 Training improves exercise capacity. Exercise has been shown to alter vascular reactivity favourably both in normal people and patients with heart failure.5 6 In chronic heart failure the resting cardiac output initially remains normal but is reduced during exercise. Also the normal physiological redistribution of blood flow to exercising muscles during exercise is decreased. This redistribution is achieved by muscular vasodilatation and splanchnic vasoconstriction. As the severity of heart failure increases both the resting and exercise cardiac output decrease and the redistribution is less, so that regional blood flow to exercising muscles and elsewhere is reduced.7 Vascular compliance is altered in heart failure. Both arterial and venoconstriction occur, and the muscular arteriolar bed becomes less able to vasodilate than normal. This is a