Cardizem SR is used in the treatment of angina pectoris (chest pain usually caused by lack of oxygen to the heart due to clogged arteries) and chronic stable angina (caused by exertion). Diltiazem is also used to treat high blood pressure. Another controlled release form, Diltiazem SR, is used only in the treatment of high blood pressure. Diltiazem, a calcium channel blocker, dilates blood vessels and slows the heart to reduce blood pressure and the pain of angina. Doctors sometimes prescribe Diltiazem for loss of circulation in the fingers and toes (Raynaud's phenomenon), for involuntary movements (tardive dyskinesia), and to prevent heart attack.