Handcuffed inmates in a Texas jail busted out of a cell... to save a guard's life.

A Parker County Jail guard was sitting in front of the prisoners' pen when he suddenly collapsed on the floor. He lost consciousness, apparently after suffering a heart attack.

"He was just talking to [the inmates], and he just kind of collapsed," Capt. Mark Arnett with the Parker County Sheriff's Office told NBC News.

"As soon as the jailer went down, they started to yell."

When their yelling failed to attract the attention of anyone upstairs, the group of eight handcuffed prisoners broke out of the cell.

They definitely saved his life. There's no doubt about that.- Capt. Mark Arnett

"They grabbed his radio and tried to radio for help," Arnett said.

Deputies upstairs heard the radio and rushed down to see what was going on. Initially they thought the inmates were inciting a riot.

"They thought it was a fight. They thought we were taking over," inmate Floyd Smith told local news station WCAA-TV. 

Once the deputies realised what was happening, they called emergency personnel, who performed CPR on the unconscious guard and used a defibrillator to shock his heart.

The jailer is reportedly in a good health and is expected to return to work today.

Capt. Mark Arnett praised the inmates for their quick action.

"They definitely saved his life. There's no doubt about that," he said.