It is current that matters, _but_ you have to understand that a supply 'capable' of delivering 6A, won't deliver 6A, unless the load is a low enough resistance to draw this. If you took the supply, and attached a 12v
1A light bulb, only 1A would flow, despite the 'capability' of the supply. 12v, can just about cause enough current to flow through the human body, to be dangerous, in the specific case, of a couple of electrodes, either penetrating the skin, or using conductive gel, diagonally placed, one each side of the heart. The 'body model' for this case, is typically about 500R.Best Wishes