The goalkeeper insists the forward has more to offer to Roberto Mancini's side's title charge and maintains his team-mates are coping under pressure
Following his £35 million move from Atletico Madrid last July, the Argentina international has scored 18 goals in 33 appearances for City this campaign.
City sit two points clear at the top of the Premier League after being Fulham 3-0 on Saturday, while Manchester United lost ground in the title race following a 3-3 draw at Chelsea.
Aguero netted a penalty and assisted Edin Dzeko's goal during the win against Martin Jol's side at the Etihad Stadium and Hart believes the 23-year-old can build even further on his displays.
“I think he [Aguero] has done great, but he can do better. He knows he can do better," Hart told reporters.
“I’m not knocking Sergio. I think he’s awesome and one of the best players in the Premier League. But I do really thinks he’s got a lot more to offer and he’ll be awesome for Man City when that happens.
“He has helped us out in important games, so that’s good, but I definitely think he can get better, and I think he knows that.
“He’s younger than me and that shocks me when I hear that. I’m being honest, I hope Sergio wants to do better and that’s going to push Man City on if he does that.”
Hart acknowledged his side are under expectations to lift silverware this season but remains confident his team-mates can channel the pressure into positive results.
“Of course we’re under pressure. We’ve got everyone knocking for that top spot, but it’s not a pressure that people are going to crumble under, it’s a pressure from being at the top of your game," he said.
“That’s the only reason people are putting us under pressure because we’re up there with the best of them, so it’s a good pressure to have.
“It makes no difference to me. I’m not going to let in goals in depending on whether there’s pressure or not.”