As I understand this, it's not the amperage that kills, but the fluctuations involved. Under normal circumstances, the Sinoatrial node
puts out about one pulse every second, causing every muscle cell in the ("lub") atria and then ("dub") ventricles to contract. Sending an electrical pulse of about 100 mV through these cells before they're done recharging from the last heartbeat could cause entire heartbeats to be missed, or cause all four chambers to contract simultaneously so that almost no blood is pumped. Enough of this sort of thing, and death is entirely feasible.
So even if a multimeter wouldn't kill in the same way as an electric chair, it could still conceivably kill. I haven't heard of this actually happening though.