Hi Anne
As Lorna says 'Deep Heat' is not recommended for RA it is more useful for muscular problems.
Ice packs can be good but wheat bags are more gentle and are possibly better at dealing with this type of inflammation. Ice packs are good for injuries where the inflammation comes on suddenly as it decreases the blood flow to the area.
Wheat bags contain things like lavender which once heated produce a long lasting heat. They come in a variety of shapes and sizes which you can apply to different parts of the body and you can even make your own! Just 'google' wheat bags and it will give you all sorts of information and where to buy!
It's best to rest the shoulder if possible, (perhaps using a sling), to help reduce inflammation. You will need to move it at intervals to stop the joint ceasing up. A case of trial and error to find what gives you most comfort.
If the problem continues you need to seek medical advice in case there is an underlying injury or perhaps a short course of anti inflammatories may help.
Good luck Anne
Lyn x