Guancydine is primarily used in the field of medicine, particularly as a vasodilator. It helps in relaxing and widening blood vessels, which improves blood flow and reduces blood pressure. This makes it effective in treating conditions like hypertension and other cardiovascular disorders. Additionally, it has been studied for its potential use in managing angina pectoris, a condition characterized by chest pain due to reduced blood flow to the heart. Its ability to enhance circulation also makes it a candidate for research in addressing peripheral vascular diseases.