DILTIAZEM treats high blood pressure and prevents chest pain (angina). It works by relaxing the blood vessels, which helps decrease the amount of work your heart has to do. It belongs to a group of medications called calcium channel blockers. Get Diltiazem ER (Tiazac) for as low as $4.37, which is 87% off the average retail price of $34.39 for the most common version, by using a GoodRx coupon.