Rocky, the two-year-old German shepherd who took two bullets trying to save his elderly owner when three masked home invaders broke into a Sydney home on Monday night, underwent an operation yesterday afternoon.

One of the bullets fired at Rocky grazed his cheek, narrowly missing his brain, during the raid in Court Street, Kingsford.

"A couple of inches to the left and he would have been toast," said specialist surgeon John Culvenor at the North Shore Veterinary Specialist Centre in Crows Nest.

This morning, the plucky dog was "looking great", a spokeswoman at the centre said.

"He's still a bit weak, but it's looking pretty good.

"We're happy with how he's going - he'll probably be here for another week."

Mr Culvenor removed the two bullets during a two-hour operation yesterday and handed them over to police for ballistic tests.

But it was Zap the rottweiler who also got Rocky through his two-hour operation - he donated half a litre of blood.

"Zap is a longtime patient of ours," said Mr Culvenor, who also installed an external stainless steel frame to help Rocky's broken leg heal.

He said Zap's owner was "a really nice guy" who brought in his substantial pet when blood was needed in an operation - which had happened on about six occasions so far.

He said Zap's help was "tremendously important".

Mr Culvenor said Rocky would make a full recovery, although he would have to stay at the surgery for at least a week and it would be up to four months before his external frame could be removed.

"Barring bad luck [such as infection], he should make a good recovery."

He said more than 20 people had offered to help fund Rocky's operation, which is likely to cost between $4000 and $6000.