The pistol reportedly shoots a dart – which can cause a heart attack once it enters the bloodstream – into its victims.
It can pierce through clothing leaves no signs of impact on the skin except a small red dot, according to insiders.
The weapon, a modified Colt 1911, is believed to have been mentioned during the infamous Church Committee probe into the CIA in 1975.
Whistleblower Mary Embree said: "The poison was frozen into some sort of dart and then it was shot at very high speed into the person.
"When it reached the person it would melt inside them, and there would be a tiny red dot on their body, which was hard to detect.
"There wouldn`t be a needle or anything like that left in the person."
Footage from the the probe in 1975 has recently gone viral after being shared by conspiracy theorists.
In the video, Senator Frank Church asks CIA director William Colby asked: "Does this pistol fire the dart?"
He replies: "Yes, it does, Mr Chairman, and a special one was developed which, potentially would be able to enter the target without perception."
Colby also reveals the toxin would not appear in an autopsy – so there would be "no way of perceiving that the target was hit".
Top secret CIA poison dart gun gives targets deadly HEART ATTACKS and leaves no trace
16 February 2016
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A WHISTLEBLOWER has claimed the CIA developed a "heart attack gun" laced with deadly poison to carry out assassinations.
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