I went into a rabbit hole reading after your comment. It seems the toxin in question (saxitoxin) is not secreted by the fish, but concentrated from contaminated

I went into a rabbit hole reading after your comment. It seems the toxin in question (saxitoxin) is not secreted by the fish, but concentrated from contaminated food, usually algae. The toxin weakens, but doesn't paralyze the heart, contrary to the respiratory system. Proper respiratory aid will help you regain full function after a few hours/days, as the toxin is excreted in the urine unchanged. There is no known antidote, or method to accelerate excretion. So the heart attack gun would be thwarted by timely but common medical care, but maybe they have better toxins these days.