A martial arts-trained man fought off four machete-wielding robbers who forced their way into his home demanding money.
The masked men broke into David Pugh's Solihull home on Tuesday also armed with baseball bats and golf clubs.
Mr Pugh, 55, who is trained in Krav Maga, said "instinct took over" when he found them attacking his 17-year-old son - and his 20-week-old puppy.
Police told him they were shocked by the level of violence used by the men.
He later took a graphic photograph of himself to highlight the extent of the injuries he suffered. [Warning: Picture follows]
The sales manager told the BBC he heard a "really big crash" and thought his son's Rottweiler puppy had knocked something over.
He left his bedroom at his home in Catherine de Barnes, and found two men attacking his son, who had his girlfriend with him.
Mr Pugh said he then helped rescue his son while also fighting off the other two men.
The father-of-two said the men kept shouting: "Where's the money? Give us your money."
"I was getting dizzy. I took quite a few blows to the head," he added.
He said the men did not take anything but "had done their homework" and avoided all the CCTV cameras.
The puppy, Zeus, was hit by the attackers and "bolted" through an open door.
Zeus has since been treated at a vets for a large cut and pneumonia.
Mr Pugh said police told him there had been a growing trend of "home invasion" style robberies.
"It leaves a nasty feel around the house. It all happened so fast," he added
"They [police] were shocked by the level of violence used."
West Midlands Police said officers were alerted to reports of a break-in at 03:09 on Tuesday "after a group of men had forced their way into the property and attacked the occupants".
Investigations are continuing and the force said it had carried out house-to-house inquiries and recovered items for forensic analysis.
Krav Maga is as a self-defence system that was originally developed for the Israeli military.