Which of the following is an antiarrhythmic medication?

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Antiarrhythmic drugs work by altering how electrical impulses travel through heart tissue to prevent or correct abnormal rhythms. Lidocaine specifically blocks fast sodium channels in cardiac cells, and it preferentially acts on depolarized, ischemic tissue. This action shortens the action potential and reduces excitability, helping to suppress ventricular ectopy and dangerous ventricular tachycardia. That makes it a useful antiarrhythmic, especially in acute settings after heart injury. The other drugs shown don’t affect heart rhythm: amoxicillin is an antibiotic, metformin is a diabetes medication, and omeprazole is a proton pump inhibitor.