Beta-blocker drug action. Computer artwork of beta-blocker drug molecules (yellow spheres) at a nerve synapse (junction between nerve cells). In the background are illustrations of hearts and electrocardiogram (ECG) traces. Beta-blockers are used to treat hypertension (high blood pressure), cardiac arrhythmias (irregular heart beat) and angina pectoris (chest pain). They act by blocking the receptors (dimples) on nerve cells for the hormone adrenaline (blue spheres) and therefore block the hormone's effects. Adrenaline has an excitatory effect on heart and blood vessel tissues, causing the heart to beat faster and blood vessels to constrict.