On Monday night someone broke into the box and stole the defibrillator, Brenton said.
The club maintained the device with help from the Red Cross.
"Red Cross has told us ... they've only ever had one stolen," Brenton said.
She said it was a shame not to have it for the benefit of the community any more.
Yesterday the Bay of Plenty Times published a story about 59-year-old Tauranga man Grant Louie, who suffered a cardiac arrest mid-serve at the Gate Pa Tennis Club and was saved by his clubmates who performed CPR and used a defibrillator.
Read more: 'He went down like a sack of potatoes': Gate Pa tennis clubmates save tennis player's life
The cost of a St John automatic external defibrillator (AED), including a servicing/maintenance package, ranges between $3000 and $3500, including GST.