Would Verapamil be useful in treating tachycardia or bradycardia and why (must explain mechanism of action) ?

It is used in treating tachycardia which is implicated in arrhythmias.

Explanation:

That is because verapamil is a calcium channel blocker. Verapamil's mechanism in all cases is to block voltage-dependent calcium channels. In cardiac pharmacology, calcium channel blockers are considered class-IV antiarrhythmic agents. Since calcium channels are especially concentrated in the sinoatrial and atrioventricular nodes, these agents can be used to decrease impulse conduction through the AV node, thus protecting the ventricles from atrial tachyarrhythmias. Calcium channels are also present in the smooth muscle lining blood vessels. By relaxing the tone of this smooth muscle, calcium channel blockers dilate the blood vessels. This has led to their use in treating high blood pressure and angina pectoris.