Which of the following is NOT one of the three main categories of antianginal agents?

Anticoagulants are indeed not classified as one of the three main categories of antianginal agents. The primary purpose of antianginal medications is to alleviate or prevent angina pectoris (chest pain due to insufficient blood supply to the heart), and they achieve this through various mechanisms.

Nitrates, beta-blockers, and calcium channel blockers are all specifically designed to manage angina. Nitrates work by dilating blood vessels, which increases blood flow to the heart and reduces the workload. Beta-blockers reduce heart rate and myocardial oxygen demand, effectively decreasing the incidence of angina episodes. Calcium channel blockers also play a role by relaxing vascular smooth muscle and reducing the force of contraction in the heart.

In contrast, anticoagulants are medications that help prevent blood clots and are used in conditions like thrombosis, stroke prevention, and certain types of heart disease, but they do not directly address the symptoms of angina or the underlying issues of myocardial oxygen supply and demand. This distinguishes them from the other three categories of antianginal agents, making them the correct answer to the question.