There are two types of calcium channels in cardiovascular system: T-type and L-type. T channels are activated by low voltage whereas L channels are activated by high voltage. T channels take 8 psec to conduct while L channels take 25 psec. T channels are involved in possible growth of cardiac muscles and pacemaker activity of SA node. L channels are involved in Ca+2 induced release, pacemaker activity of SA node and AV conduction. Unlike L channels, T channels have no effect on ventricular and intestinal contractions. In smooth muscles, T channels undergo pharmacomechanical coupling whereas L channels experience excitation-contraction coupling. All calcium-channel blockers inhibit the activity of L channels whereas only mibefradil is known to inhibit the activity of T channels.