The basic pharmacological action of calcium antagonists is to inhibit the entry of calcium ions into cells, but different types of calcium antagonists have different sites of action and different selectivity for cardiac myocytes and vascular smooth muscle cells, which exhibit effects mainly on cardiac conduction and cardiac contraction and inhibition of vascular tone. In addition to known hypersensitivity reactions, calcium antagonists should be contraindicated in patients with hypotension, congestive heart failure, sick sinus syndrome, and second- or third-degree conduction block, while dihydropyridine calcium antagonists should be avoided in patients with marked vasodilation and decreased vascular resistance, severe aortic stenosis, and hypertrophic cardiomyopathy, and in patients with prolonged Q-T intervals and a history of severe ventricular arrhythmias. Dihydropyridine calcium antagonists and diltiazem should be used with caution in patients with prolonged Q-T intervals and a history of severe ventricular arrhythmias. The combination of calcium antagonists should be used with caution.