There are two things here. Firstly call them, thank them for the interview, ask if there has been any decision yet, and ask if there is a likely timeline if not.
It can help to vaguely mention other things look like they may be moving, so you're keen to make sure the one's you're interested don't get missed (so you get the message to them you are keen).
After that it's a waiting game, you can touch base again in a week or so to keep showing your interest.
My second point though is to keep looking. You may have had a great interview, great rapport with the interviewer(s), etc, but the cold hard fact is that a million and one things may have happened:
- An internal candidate may be on a "promise" and you were there to make up numbers,
- The budget could be canned,
- Someone may offer 90% of what you do, but only wants 60% of the money,
- Or worst of all, as well as you did, maybe someone did even better. It can happen that you do nothing wrong, but you're still second (you may have broken the world record, but here comes Usain Bolt to smash your new record).
A week is a long time to wait with nothing, and yes, from experience I've had decisions that HAVE taken much longer. Usually though, if you are in the frame for the role, there will be some kind of comms to keep YOU interested (even if only to say "we're still discussing it"). If they have delays their end they will be afraid that their favoured candidate will pick up another offer, so they will usually keep in touch, even if they can't say why the delay is happening.
So talk to them, but treat it as a No until you get confirmation otherwise and keep looking.