Up to four defibrillators, valued at $5000 each, were taken after two males smashed a window to gain entry to a van at the ambulance service's headquarters in Forster Road about 4am on January 20.

St John's state officer Brett Aimers couldn't guess at a motive for the "pathetic act".

"Maybe they're trying to sell them. They can't be used for anything other than to save lives."

He said the semi-automatic equipment, which emitted large electric shocks to revive patients from cardiac arrest, couldn't be misused for pranks or to endanger life.

"A lethal heart rhythm has to be present before it delivers energy to a patient."

Although the service has spare defibrillators, Mr Aimers said the ambulance service's capacity to save lives was potentially reduced.

He said buying replacements would also steal from funds normally allotted for buying first aid stocks and maintaining the fleet of ambulances.

Information to Crime Stoppers on 1800333000.