The heater plus what other 120 volt devices were running may have overloaded the circuit.
Check the circuit breakers in the main circuit breaker panel.
Switch each one "off" then back "on". This should restore 120 volt power to the GFI outlet.
Push the "test" button on the GFI outlet.
GFI should trip to "off".
Push the "reset" button.
Power to all the outlets should now be "on".
If you cannot get the GFI outlet to trip and reset, the outlet may need replacing. There are other possible failure modes as well.
I wish you good luck and happy trails ahead!