Heng's levels of political support appear to have been limited up until 1970; aside from being President of the Assembly, he had previously been director of the main Phnom Penh prison.

This was a largely ceremonial role, as Lon Nol had assumed most of the Head of State's political powers on an emergency basis: Sihanouk, from exile, was to dismiss Heng as an "insignificant puppet".

[6] Apart from giving press conferences, State Chief Cheng Heng was also called on to receive visiting foreign politicians: William Shawcross relates an incident during Spiro Agnew's July 1970 visit to Phnom Penh, in which that President Cheng Heng was forced to contend with United States Secret Service personnel training their guns on him while he was attempting to welcome Agnew to the Royal Palace.

[7] Nol subsequently used a political crisis to remove Head of state Cheng Heng from power and take over the role himself early in 1972.

In 1975, with the Khmer Rouge forces surrounding the capital, Heng's name was published on a list of "Seven Traitors" (also including Lon Nol, Sisowath Sirik Matak, In Tam, Long Boret, Sosthene Fernandez and Son Ngoc Thanh) who were threatened with immediate execution in the event of a Communist victory.