What is the primary effect of vasodilators?

Vasodilators primarily cause the relaxation of vascular smooth muscle, which leads to the widening or dilation of blood vessels. This dilation results in a decrease in vascular resistance, which in turn lowers blood pressure. As blood vessels become wider, the same volume of blood can flow through them with less resistance, resulting in reduced pressure against the walls of the arteries. This mechanism is particularly beneficial in treating conditions such as hypertension, where controlling blood pressure is crucial.

The other effects mentioned, such as increasing cardiac output or altering heart rate, are not direct effects of vasodilators. Typically, vasodilators can actually lead to a reflex increase in heart rate as the body attempts to maintain adequate blood flow, but this is a compensatory response rather than a primary effect. Similarly, while these agents reduce vascular resistance through dilation, they do not inherently increase vascular resistance; in fact, the opposite occurs.