β-blockers are contraindicated in patients with severe bradycardia (heart rate less than 50 beats/min) or atrioventricular (AV)

 conduction defects in the absence of a pacemaker.

β-blockers should be used with particular caution in combination with other agents that depress AV conduction (eg, digoxin, verapamil, and diltiazem) because of the increased risk for bradycardia and heart block.

Relative contraindications include asthma, bronchospastic disease, and severe depression. β1 -selective blockers are preferred in patients with asthma or chronic obstructive pulmonary disease. However, selectivity is dose dependent, and β1 -selective agents may induce bronchospasm in higher doses.

All β-blockers may mask the tachycardia and tremor (but not sweating) that commonly accompany episodes of hypoglycemia in diabetes.

Non-selective β-blockers may alter glucose metabolism and slow recovery from hypoglycemia in insulin-dependent diabetes.

β-blockers are negative inotropes (ie, they decrease cardiac contractility). Therefore, β-blockers may worsen symptoms of heart failure in patients with left ventricular dysfunction (ie, ejection fraction less than 40% [0.40]) and initiation or titration should be delayed in patients with acute heart failure until symptoms have resolved.