Thieves smashed open a defibrillator case in Wrexham before making off with a mask and pads.
The window pane of the box outside Active Heatlh on Coedpoeth High Street was smashed at some point in the last seven days before the items within it were stolen.
The defibrillator itself was left behind, but has now had to be taken out of action.
Police described the crime as "despicable".
A spokesman said: "A defibrillator box has been broken into outside Active Health, High Street, Coedpoeth sometime in the last seven days.
"We are appealing for anyone who has information about this crime to contact us on 101 quoting reference Y115212."
In a post shared on the Coedpoeth community Facebook group, Active Health, a chiropractic and sports massage clinic, said the incident had been a burden during a time when they were preparing to reopen after lockdown.
A spokesman said: "The defib case was broken into last week and the pocket mask and extra pad pack was stolen.
"Fortunately the defibrillator itself was left, presumably because it couldn’t fit through the window aperture.
"For now, I have removed the defib and have it inside the building for safekeeping.
"I did add a sign stating where the nearest was for now (Park Road) but that too has been removed."
They said a local firm had agreed to replace the broken pane for free, but they were still trying to find replacement equipment to put back into the box.
They added: "We’ve been working really hard to prepare the clinic for re opening and frankly this is an extra burden we could do without.
"In the event of a cardiac arrest, the chances of a successful outcome fall by approximately 10% for every minute that CPR and defibrillation is delayed.
"I sincerely hope that the extra time taken in the event of it being required do not mean the difference, quite literally, between life and death."
The company were approached for further comment.
