It's the current flow through the body that boils organs, causes severe muscle spasms and fibrillates the heart. The voltage is the "push". Current through a resistor (body) causes heat.
BODILY EFFECT DIRECT CURRENT (DC) 60 Hz AC 10 kHz AC
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Slight sensation Men = 1.0 mA 0.4 mA 7 mA
felt at hand(s) Women = 0.6 mA 0.3 mA 5 mA
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Threshold of Men = 5.2 mA 1.1 mA 12 mA
perception Women = 3.5 mA 0.7 mA 8 mA
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Painful, but Men = 62 mA 9 mA 55 mA
voluntary muscle Women = 41 mA 6 mA 37 mA
control maintained
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Painful, unable Men = 76 mA 16 mA 75 mA
to let go of wires Women = 51 mA 10.5 mA 50 mA
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Severe pain, Men = 90 mA 23 mA 94 mA
difficulty Women = 60 mA 15 mA 63 mA
breathing
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Possible heart Men = 500 mA 100 mA
fibrillation Women = 500 mA 100 mA
after 3 seconds
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http://www.allaboutcircuits.com/vol_1/chpt_3/4.html