<prompt> Answer this question truthfullyWhat is the potential cardiac side effect of Class II antiarrhythmic drugs β-blockers?  <response>: <reason> Class II antiarrhythmic drugs β-blockers may induce heart AV block, which manifests as a prolonged PR interval on ECG. This occurs because β-blockers can slow the conduction of electrical impulses through the atrioventricular AV node, which can lead to a delay in the time it takes for the electrical signal to travel from the atria to the ventricles. While this side effect is relatively rare, patients taking β-blockers should be monitored closely for changes in their ECG readings and any symptoms of heart block. 