Exactly. If you create a 9v voltage between an artery and a vein (though 0.1v is plenty) and you generate more than around 160mA current (any battery and static electricity can do that).

Essentially you'd have to get a conductor into an artery and one into a vein, and if there is a millisecond where both are in there but not touching the skin your heart will stop. It can be restarted for a minute or so afterwards, but it won't restart on it's own.

Your skin has a "safe" (more or less) conductive layer to prevent this from occurring, with another layer with enormous insulation below that. That's why humans usually survive getting hit by lightning, yet succumb to such a stupid tiny amount of current if it gets past the skin.