Beta blockers or beta-adrenergic blocking agents are certain drugs used to treat a variety of heart conditions and other diseases. They block the action of beta-type adrenergic receptors in the body. The hormone epinephrine (adrenaline) stimulates the sympathetic nervous system by acting on these receptors.
There are two types of beta receptors: beta 1 receptors located mainly in the heart, and beta 2 receptors located all over the body, but mainly in the lungs, muscles and arterioles.
If epinephrine acts on beta 1 receptors, the heart rate and the blood pressure increase, and the heart itself requires more oxygen. Drugs that block these beta 1 receptors therefore have the opposite effect: they lower the heart rate and blood pressure and are useful when the heart itself is deprived of oxygen. They are often prescribed after heart attacks.
Non selective beta blockers should not be used in patients with Asthma or any reactive airway disease. Doing so can block the effects of Beta-2 agonists such as albuterol.