The calcium channel antagonists interfere with cellular calcium uptake. They cause arterial dilatation and, to a varying extent, depression of myocardial contraction and conduction. They also have an intrinsic diuretic effect. These actions are useful, not only in the management of hypertension and angina, but also for supraventricular arrhythmias (verapamil) and peripheral vasospasm (dihydropyridines). The adverse effects are dose-dependent. They include flushing, headache and peripheral oedema (particularly with the dihydropyridines) due to vasodilatation, and depression of myocardial function (particularly verapamil and, to some extent, diltiazem). The shorter-acting dihydropyridines (particularly nifedipine) can cause reflex-mediated cardiac stimulation which may be dangerous. The availability of slow-release and longer-acting formulations has improved tolerability and compliance, although the effect of these newer preparations on outcome is currently unclear.