A single punch landed an amateur boxer with 42 weeks in prison.
Jacob Fairfoot-Milton was looking to reclaim a loan from Jamie Coole, Bristol Crown Court heard.
But when he failed to find him he punched Mr Coole's 63-year-old father Stephen to the face.
The formidable blow left Mr Coole with a broken tooth, facial swelling and bruising.
He was also diagnosed with a heart murmur and leaking heart valve, which he could have sustained as a result of the attack.
Fairfoot-Milton, 26, of Broad Weir, Bristol, pleaded guilty to assault occasioning actual bodily harm on June 9.
Judge Mark Horton told him: "This was an unprovoked attack on a 63-year-old man inside his own address.
"It left him with both physical and obvious psychological effects."
Susan Cavender, prosecuting, told Bristol Crown Court Fairfoot-Milton entered Mr Coole's home on two occasions, looking for Jamie Coole.
On the second occasion Stephen Coole went to usher him out and received a catastrophic blow which knocked him backwards.
Fairfoot-Milton then fled on a mountain bike, the court heard.
Mr Coole made an impact statement saying the assault left him distraught and feeling unsafe in his own home.
The court heard Fairfoot-Milton had previous convictions for violence which included ABH as well as assaulting police and public order offences.
Ian Kelcey, defending, said his client had loaned Jamie Coole £200 and had not been paid back.
Mr Kelcey said Fairfoot-Milton's girlfriend described him as "kind, thoughtful and supportive".
He urged the judge to suspend immediate custody.
Mr Kelcey said: "It was not a prolonged assault.
"It was one punch.
"I accept it was from a man whose had some training in boxing."
