Fight or flight? You never know what you will do in a dangerous situation until you're in it.

Jan Cooper, 72, got her answer when she faced down an intruder with her .357 magnum.

(KABC/ABC News)

Around 12:30 a.m. on Sunday morning, Capo, the family Rottweiler, started barking. Cooper wasn't initially alarmed because her Anaheim, Calif., home is near a 7-Eleven store and Capo often barks at the pedestrian traffic, she told ABC News.

Then the barking became louder, more aggressive and non-stop.

Only Cooper and her 85-year-old husband, Bob Cooper a World War II veteran and former O.S.S. officer who now uses a wheelchair, were in the house.

Jan Cooper called the police and grabbed her gun.

"I have no idea what's happening but I don't like the sound of that dog," Cooper said, sounding out-of-breath and alarmed on the 911 tape obtained by ABC News affiliate KABC.

Cooper told ABC News that she peeked between the window slats near her front door and saw the silhouette of a person outside.

"Your heart goes up into your throat," she said.

Still talking to a dispatcher, Cooper noticed Capo's attention divert to the side of the house, and she knew the intruder was on the move.

Cooper said she then headed to the kitchen to turn on the back floodlights.

Before she could do so, she found a man trying to open her sliding door.

"The minute the door started to slide open, I fired," Cooper told ABC News.

"Back up you son of a b****! Back up!" Cooper roared on the 911 tape.

Cooper, who considers herself a Christian woman, said she was surprised by her reaction.

"I don't curse. But after I shot, rage took hold," she told KABC.

Cooper barely missed the intruder, according to Orange County Sherriff's Department spokesman Jim Amormino. He told ABC News that trajectory would have put the bullet somewhere between the intruder's mouth and the top of his head if he had gotten through the sliding door.

Deputies quickly arrived on the scene, Amormino said, setting up a perimeter and soon apprehending Brandon Alexander Perez.

At his arraignment on Tuesday, Perez pleaded not guilty to the charge of first degree burglary, according to Chris Kim from the Public Affairs Unit of the Orange County District Attorney's Office.

Perez, who had a prior burglary conviction and had been living in a halfway house on parole, remained jailed on $50,000 bail, authorities said.

They added that Perez had not been assigned a permanent attorney from the public defender's office.

The public defender who represented Perez at his arraignment could not immediately be reached for comment.

Meanwhile, Cooper, a grandmother who hosts an Internet talk show dedicated to Rottweilers and writes poems about her favorite breed, believes she will not have to guess at what she would do if her home or family is ever threatened again.

"I do know now," Cooper told KABC. "I will protect myself rather than freeze or panic. … I do have a capability to take action."