Tiazac (Diltiazem ER, Cardizem CD, Cardizem SR, Cardizem LA, Dilacor XR, Cartia XT, Diltia XT, Taztia XT) is a calcium-channel blocker. It affects the amount of calcium found in your heart and muscle cells. This results in relaxation of blood vessels, which can reduce the amount of work the heart has to do and reduces high blood pressure.