A vasoactive substance is an endogenous agent or pharmaceutical drug that has the effect of either increasing or decreasing blood pressure and/or heart rate through its vasoactivity, that is, vascular activity (effect on blood vessels).
In the context of cardiovascular physiology, a substance that modulates the activity of blood vessels can be considered vasoactive. This effect may manifest as an increase or decrease in blood pressure and/or heart rate, depending on the specific substance and its mechanism of action.