The 18-year-old was given the nod to start at short notice and Archibald was pleased with how he coped against 63-times capped Alex Tziolis and Africa Cup of Nations winner Arnaud Djoum.
“I was delighted with young Andy in there,” Archibald said.
“He only found out he was playing on Saturday morning.”
McCarthy’s only other start in the Premiership this term was in the 1-1 draw at Celtic Park in April and Archibald’s faith in the youngster will have been further boosted by his display at Tynecastle on Saturday.
‘Massive credit to Andy’
“We had a lot of injuries and had to bring Andy McCarthy into the middle of the pitch, as well as putting Kris Doolan in a wider area, so I think it was a fantastic performance in the circumstances,” the manager added.
“We had decided to go with Liam Lindsay on the Friday, but Liam had to pull out with a dead leg.
“We had worked on a completely different shape and we had to change that on the day of the game, so it’s a massive credit to Andy for adjusting and performing so well.”
The Jags hit the front against Hearts thanks to a second-half Doolan header following fine work from Steven Lawless.
Thistle’s Daniel Devine was then penalised for a handball in the box, earning a second yellow card and an early bath in the process, with Esmael Goncalves converting the resulting spot-kick.
Lawless restored the visitors’ lead before Andraz Struna’s late close-range finish earned Hearts a point.
“My concern at Kilmarnock was that, for all the control we had, we never hurt them enough,” Cathro said.
“That wasn’t a problem against Partick Thistle. The only thing missing was us putting the ball in the net and scoring goals. I think that’s a game that the majority of times we play it we would win.
“We are making progress, but we have to prove it – and it’s the results that do that.”