Diltiazem is an orally and intravenously active calcium channel blocking agent shown to be an effective and well-tolerated treatment for stable angina and angina due to coronary artery spasm. Its efficacy in these diseases has generally been similar to that of nifedipine or verapamil - alternative calcium channel blockers with which diltiazem has many electrophysiological, haemodynamic, and antiarrhythmic similarities. The antianginal mechanism of diltiazem cannot be precisely described; however, it appears to increase myocardial oxygen supply and decrease myocardial oxygen demand, mainly by coronary artery dilatation and/or via both direct and indirect haemodynamic alterations. Diltiazem has also shown substantial efficacy in the treatment of unstable angina, hypertension, and supraventricular tachyarrhythmias, but further study is necessary before its place in the treatment of these diseases may be clearly established. Although headache due to peripheral vasodilatation and depression of atrioventricular nodal conduction may be troublesome, side effects occur in only 2 to 10% of patients receiving diltiazem and are generally minor in nature. Thus, diltiazem offers a worthwhile alternative to other agents currently available for the treatment of angina pectoris. Although the infrequency of serious side effects may offer an advantage, its relative place in therapy compared with that of other calcium channel blockers remains to be clarified.