Mancini has made it clear the England number one will not be in his starting line-up to face Wigan at Wembley on Saturday, preferring to reward Costel Pantilimon for his performances in getting City to Wembley.
The Romanian has played in all of City's domestic cup fixtures this season, and Mancini believes it would be unfair to alter his selection policy, despite Hart's disappointment.
When asked if he may be tempted to pick Hart for the final, the Italian said: "I don't think so, we decided this at the start of the season. Pantilimon deserves to play.
"Joe won the FA Cup two years ago, he won the Premier League last year, he is the best keeper in England and I think he should be happy his second keeper can play in a big game.
"I know he wants to play but we decided at the start of the season it was important for Pantilimon to play in the two cups."City stuttered to a goalless draw with Swansea on Saturday, with Edin Dzeko and David Silva missing great chances to claim all three points.
Mancini admitted Dzeko's miss from four yards summed up a season where City's lack of goals has cost them; the Blues have found the net 61 times so far this season, compared to 87 at this stage last term.
But the Italian does not believe the decision to sell Mario Balotelli to AC Milan in January played a part in their failure to retain the league title.
Balotelli had scored just two league goals before moving to the San Siro, but has been in prolific form since, scoring eight in nine appearances.
Mancini said: "For Mario it was better to go back to Italy and even with Mario I think the season would have been the same."
He added: "It is difficult when you consider why you don't score enough goals. Last year we scored 20 goals more than this season and we are missing them, it's too many.
"If we had scored another 10-20 goals we could have been fighting for the league."
But Mancini was cagey when asked if a striker was on his summer shopping list.
"We can't know which player can score 25 goals next year. If we knew that we would be magicians," he said.
"We have good players and were unlucky this season. Now it is important we win the FA Cup and then try to improve our team."
Source: Manchester City MAD