vasodilator /vā′zōdī″lātər/ [L, vas + dilatare] , a nerve or agent that causes dilation of blood vessels by promoting the relaxation of vascular smooth muscle. Chemical vasodilators include hydralazine, nitroglycerin, nitroprusside, nesiritide, and trimethaphan. They have been useful in the treatment of acute heart failure in myocardial infarction, in cases associated with severe mitral regurgitation, and in failure resulting from myocardial disease.