The Avengers aren't that concerned about the arc reactor in Tony's chest even though they should be, did Tony tell them?
The only on screen conversation we have is between Bruce and Tony when they're having a little bit of a verbal contest.
Bruce Banner: Ah, see. I don't get a suit of armor. I'm exposed, like a nerve. It's a nightmare.
Tony Stark: You know, I've got a cluster of shrapnel, trying every second to crawl its way into my heart. (points at the MINI-ARC REACTOR in his chest) This stops it. This little circle of light. It's part of me now, not just armor. It's a... terrible privilege.
Bruce Banner: But you can control it.
That doesn't mean they don't talk about it off-screen. In fact they most probably do in a similar manner to Tony with Bruce. However, the audience doesn't need to see that, we've already had the mini catch up scene with Bruce and a whole origin film on it.
I'm not sure why anyone would really need to be worried by it in his chest. It keeps him alive and powers his suit but seems to be very well protected having lasted a lot of fights. If anything Tony is more protected than the rest of them, having a fancy protective suit.