“What medication is given to lower heart rate?”

Beta blocker

Instead of just treating a high rate it is important to elicit the cause of the elevated heart rate. If it is "sinus tachycardia" the causes include pain, anemia, dehydration, infection, low oxygen level, stress, deconditioning, fever, hyperthyroidism among many others. If the rhythm is atrial fibrillation the classes of drugs that lower heart rate include beta blockers, negative chronotropic (heart rate slowing) calcium channel blockers, Digoxin, and anti-arrhythmic drugs such as Sotalol (potassium channel blocker) and Amiodarone (multiple class effects-beta blocker, calcium channel blocker, potassium and sodium channel blocker).