Vasodilators are pharmacological agents that induce relaxation of vascular smooth muscle, leading to the widening of blood vessels and a decrease in systemic vascular resistance. They are crucial in managing conditions such as hypertension and heart failure, as they improve blood flow and reduce cardiac workload. A key example is nitroglycerin, commonly used in acute coronary syndromes, while potential complications include hypotension and reflex tachycardia.