Effect of electrocution on the heart

I know that small currents passing directly through the heart during electrocution can cause fatal arrhythmias, but I was wondering today:
wouldn't the heart muscle seize up just as skeletal muscles do in the body when current from electrocution passes through them? If not, why not? And if so, what are the effects? Does it damage the heart, or just prevent it from operating, or what? I was thinking that if it does happen, with all the blood and chambers involved, hydraulic pressures might permanently rip something or something like that.

So what's the straight story?

I have no idea as to the answers to your questions but it scares me to think that anyone really wants to know

What have you got in mind?

I know the heart has its own complicated system for activating muscle, with specialized fibers and what-not substituting for the usual straightforward nerves. Does this mean that heart muscle doesn't respond the same way to direct electrical stimulation as other muscles would? Would it scrunch up in violent contraction, or just go rigid, or just vibrate, or what? Does this ever even happen in electrocution (I've never seen any references to anything like this, only arrhythmias).

Why? I was thinking about people getting electrocuted by touching wires and stuff (after thinking about the risks of lightning strikes shortly prior to that), and from there I considered the effects of electrocution, namely, the tendency for skeletal muscles to contract, which prevents a victim from letting go of a wire, and also causes suffocation through a similar mechanism. Now, I've never heard anyone say anything about the heart undergoing a massive contraction in the same way; instead it's always said that arrhythmias are what cause the troubles. But it seems logical that the heart would contract indiscriminately and abruptly if current passes through it as well.

Whence my curiosity, and my question. I wasn't planning to throw a radio into anyone's bathtub.