Calcium channel blocker effect. Conceptual computer artwork of calcium ions (orange) controlling blood flow through the blood vessels (springs) of a human heart. Calcium channel blockers are drugs used to treat angina pectoris (chest pain) and high blood pressure (hypertension) as they can target calcium channels in smooth muscle, such as found in the heart and blood vessels. By preventing the uptake of calcium, they prevent the muscle from contracting, which improves the circulation of blood through the heart and reduces blood pressure. Here, fewer calcium ions at the central blood vessel has resulted in a relaxed blood vessel wall and a reduction in blood pressure.