Generally, beta blockers prevent stimulation of the beta-1 adrenergic receptors and also affect the beta-2 adrenergic receptors. Beta-1 adrenergic receptor inhibition blocks the sympathetic stimulation of the heart and thus decreases the myocardial oxygen demand whereas their action on beta-2 adrenergic receptors can potentially cause bronchoconstriction. Cardioselective beta blockers are 20 times more potent at blocking beta-1 receptors than beta-2 receptors. They are therefore less likely to cause bronchoconstriction compared with non-selective beta-blockers. Examples include metoprolol, bisoprolol and carvedilol.