B

Metoprolol (a β-blocker) and verapamil (a non-dihydropyridine calcium-channel blocker) both depress the SA and AV nodes. When given together their negative chronotropic and dromotropic effects are additive, frequently leading to marked sinus bradycardia and varying degrees of atrioventricular (AV) block rather than tachyarrhythmias or torsades. Case reports describe complete heart block and cardiogenic shock after this combination [Lee, 1995, PMID 7785794; Wayne, 1982, PMID 6127992].