It Really depends on a lot of factors so it's more about what other symptoms you have when it's fast. Usually at rest if it over a hundred for any length of time I would consult a Doctor. Now for me I had a condition called VT which basically my heart would go into a quiver action and if you felt your puse it could be as his 200. But mine had a tendency to happen even at 120. So I would put a number as this is fast because when your working hard or exercising it can get well up in the 160s. But with me I would also get short of breath and this was because when in that quiver state now blood is flowing and it feels like your not getting any air.
Are you concerned about a higher heart beat? I know typically when a doctor sees it over 100 they will recheck it after a little time and see if it comes down. At rest I know they like it to be between 70 and 80 I'd memory serves. Does that answer your question?