When you say power cord, do you mean the wire itself is unusually warm to touch or just the connector, the part of the power cord that gets plugged into the socket?
Power cord (the wire) getting very hot is very bad. I think it may be the heating element that has shorted somewhere and this increases the current which is what heats the cord. If the heating element is a serviceable part on your heater, it needs to be replaced.
If the connector gets hot, see if you can try it in a different socket, a one on a breaker with the same current rating that is. There may be a bad connection in the original socket. It is also possible that the connector on the power cord has a lose screw or otherwise lost good contact with either live or neutral wires which increases its internal resistivity hence the extra heat.
It always helps when you post the model number of the device in question.