In heart failure, particularly when cardiac output is significantly reduced, arterial vasoconstriction helps to maintain arterial pressure. The increased systemic vascular resistance, however, contributes to an increase in afterload on the heart, which can further depress systolic function.

Does Arteriole constriction increase or decrease afterload does venous constriction increase or decrease preload?

Constriction of venous (capacitance) vessels increases venous blood pressure and increases cardiac preload and cardiac output by the Frank-Starling mechanism, which increases arterial pressure. Because vasoconstrictor drugs increase arterial pressure, they comprise a functional group of drugs known as pressor drugs.

Does vasodilation increase afterload?

In the setting of systolic failure, judicious vasodilation reduces vascular resistance and, potentially, afterload, allowing stroke volume to increase.