Pak n' Save staff at Silverdale used a defibrillator and carried out chest compressions on a male customer after he suffered a suspected heart attack in his car.
The incident happened this morning in the supermarket's car park.
A Foodstuffs spokeswoman said first aid-trained staff used the defibrillator which was kept in all the chain's stores and carried out chest compressions on the man till emergency services arrived.
An ambulance spokesperson said a patient in his 40s was dead when ambulance personnel arrived.
Eyewitnesses posted about the incident on Facebook.
