Platt has defended Mancini over the Italian's outburst at the end of Tuesday's controversial Champions League draw with Ajax at the Etihad Stadium, claiming the incident has been exaggerated.
Mancini confronted the referee after City had a late goal disallowed and were denied a penalty, and also clashed with a cameraman.
There had been fears Mancini could incur a touchline ban for his actions but the matter was not reported to European governing body UEFA by referee Peter Rasmussen or the match delegate.
First-team coach Platt, who played alongside Mancini at Sampdoria, said: "He has always been like that -- as a player he was completely like that.
"Monday to Friday he was fine but once he is on a pitch, if things don't go well for him -- he has this fire in him. That is what he believes in.
"People make a great deal about it. It is not the first time he has reacted in that way, not necessarily at Manchester City.
"He wears his heart on his sleeve. If he has got something to say he will go and say it."
The media pressure has increased on Mancini in recent weeks with City's form yet to reach the heights of last season.
The latest incident came a day after Mancini lost his temper in a press conference following a question that referred to his previous statement that he was "close to seven or eight teams" last season.
Meanwhile, Joe Hart has nothing but respect for the Premier League goalkeeping union's most senior representative Brad Friedel.
Sixteen years spans the two men who could well be in opposition when City take on Spurs tomorrow.
But the England number one was full of praise for 41-year-old American Friedel -- who last May became the oldest player to appear in a competitive match for Tottenham.
"Brad's a shining light and a great example. What he has done is pretty special, something I don't think many people will be able to achieve," he said.
"He's done great things and I don't think age really concerns him."
Asked if he would like to emulate the American, Hart added: "At the moment, I just want to get to 26, if I'm honest! I don't really look into the future that much -- I never have done and never will do."