Diltiazem, sold under the brand name Cardizem among others, is a calcium channel blocker medication used to treat high blood pressure, angina, and certain heart arrhythmias. It may also be used in hyperthyroidism if beta blockers cannot be used. It is taken by mouth or injection into a vein. When given by injection, effects typically begin within a few minutes and last a few hours. Common side effects include swelling, dizziness, headaches, and low blood pressure. Other severe side effects include an overly slow heart beat, heart failure, liver problems, and allergic reactions. Use is not recommended during pregnancy. It is unclear if use when breastfeeding is safe. Diltiazem works by relaxing the smooth muscle in the walls of arteries, resulting in them opening and allowing blood to flow more easily. Additionally, it acts on the heart to prolong the period until it can beat again. It does this by blocking the entry of calcium into the cells of the heart and blood vessels. It is a class IV antiarrhythmic. Diltiazem was approved for medical use in the United States in 1982. It is available as a generic medication. In 2020, it was the 76th most commonly prescribed medication in the United States, with more than 9million prescriptions. An extended release formulation is also available. Medical uses Diltiazem is indicated for: Stable angina (exercise-induced) – diltiazem increases coronary blood flow and decreases myocardial oxygen consumption, secondary to decreased peripheral resistance, heart rate, and contractility. Variant angina – it is effective owing to its direct effects on coronary dilation. Unstable angina (preinfarction, crescendo) – diltiazem may be particularly effective if the underlying mechanism is vasospasm. Myocardial bridge Dysmenorrhea For supraventricular tachycardias (PSVT), diltiazem appears to be as effective as verapamil in treating re-entrant supraventricular tachycardia. Atrial fibrillation or atrial flutter is another indication. The initial bolus should be 0.25 mg/kg, intravenous (IV). Because of its vasodilatory effects, diltiazem is useful for treating hypertension. Calcium channel blockers are well tolerated, and especially effective in treating low-renin hypertension. It is used as topical application for Anal Fissures as it promotes healing of fissures due to its vasodilatory property. Contraindications and precautions In congestive heart failure, patients with reduced ventricular function may not be able to counteract the inotropic and chronotropic effects of diltiazem, the result being an even higher compromise of function. With SA node or AV conduction disturbances, the use of diltiazem