What is the difference between selective and nonselective beta blockers?

Selective beta blockers, also called cardioselective, primarily block beta-1 receptors in the heart, reducing heart rate and contractility without significantly affecting beta-2 receptors in the lungs and blood vessels. Metoprolol and atenolol are selective. Nonselective beta blockers like propranolol and nadolol block both beta-1 and beta-2 receptors, which can cause bronchospasm in patients with asthma or chronic obstructive pulmonary disease. Selectivity is dose-dependent and diminishes at higher doses.