Put the heat on (idea)

1. To point a pistol at. "I threw the benny (overcoat) over the arm to cover the biscuit (gun), put the heat on him right on the stem (street) and snatched the boodle (money)." 2. To intensify police activity within a given area or throughout the underworld generally; to spur an anti-crime campaign; to publicize racket operations; to begin a widespread hunt for a wanted criminal. 3. To apply drastic measures, especially upon prospective victims of extortion.

- american underworld dictionary - 1950