Did you remove only the nuts or did you remove the nuts and the cleats. If you haven't removed the cleats, thats whats holding the wheel on. For safety sake, to remove the cleats, put the nuts back on several turn and hit the side of the cleats. Quite often the cleats will jump off with enough force to hurt someone. The nuts serve to hold the cleats on so they can be safely removed. If you do have the cleats removed and it is stuck, see how close the valve is to one of the spokes. There are safety stops near the valve on the wheel. If someone installed the wheel with one of the stops on a spoke, it will take a pretty good size hammer. Heat will do no good and all you will do is take a chance of ruining something.