NAPA (CBS SF) — Napa police are on the lookout for a robbery suspect who attacked a jewelry store worker.

The incident happened Monday at Napa Valley Jewelers at the town mall on First Street.

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Police say two men entered the store wearing masks and began assaulting the employee.

Store owner Kent Gardella wasn’t sure what was happening when the men entered his store.

“I looked up and two guys came in wearing masks, and I thought it was a joke,” Gardella said.

Store employee Bob Porter was punched and struck with a pair of pliers. Porter suffered cardiac arrest during the attack.

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“He was hitting him, and hitting him, and hitting him,” Gardella said.

Gardella jumped into action, grabbing a stainless steel ring sizing tool into a makeshift baton, hitting one of the suspects in the leg.

Emergency responders administered CPR to Porter and transported him to Queen of the Valley Medical center where he is in critical condition.

Police tracked one suspect to a nearby parking garage. The other, a juvenile is still at large.

Police say he is 17-years-old, has brown hair, 5 feet 11 inches tall and weighs about 200 pounds.

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It is unknown whether any merchandise was taken from the store.