Fundamental differences in the pharmacodynamic and pharmacokinetic profiles of β-adrenergic blocking agents must be considered in optimizing their efficacy and determining the appropriate selection of these drugs in different patients. Beta blockers are contraindicated in patients with asthma and should be used cautiously in heart failure. Clinically important distinctions are related to whether a β blocker is β₁-selective or nonselective. Most adverse effects of β-blocker use are related to interference with β₂-mediated functions including bronchodilation, vasodilation, and mobilization of free fatty acids. To achieve the potential benefits of β₁ blockade (decreased heart rate, blood pressure, cardiac workload, and excitability), a low plasma concentration of a β₁-selective drug is required. Adverse effects of β blockers can be further decreased by selecting a sustained-release β₁-selective drug. Beta blockers are further differentiated on the basis of lipophilicity or hydrophilicity. Lipophilic β blockers cross the blood-brain barrier, whereas hydrophilic agents do not enter the central nervous system. Some lipophilic agents (metroprolol, timolol, and propanolol) have been shown to decrease mortality in coronary heart disease, particularly sudden cardiac death.