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A Contra Costa firefighter suffered a cardiac arrest while on duty on Monday afternoon, fire officials said.
The fire department said Contra Costa Fire Engineer Don Danielson was at the Concord station at when the arrest occurred at about 4:12 p.m.
A paramedic and fire engineer from Danielson's crew and a nurse used a defibrillator to shock him and performed CPR. After a minute or two of CPR, he regained a pulse and began to breathe on his own again, the fire department said.
He was transported to a hospital, where he woke up Monday night.
The fire department said cardiologists are optimistic Danielson will make a good recovery.
