If its a reasonably sophisticated helicopter with decent autopilot, the previous replies aren't really correct because the autopilot will mask these basic effects. What I would expect to happen (hands off the cyclic) is that the aircraft yaws, but with minimal change in roll or pitch attitude. Initially the track will remain as it was, but the force of the air hitting the side of the heli will gradually change the track until it is the same as the heading (assuming no wind). You would initially see a large deflection in the slip ball representing the lateral acceleration (ie rate of change in track) but this would gradually subside as the track came closer to the heading.