Hi there..First I would be inclined to have him ckecked over by your vet better to be safe then sorry,if the vet gives him the ok,ask him about your problem he will be able to give you the best advice and put your mind at rest.good luck with him.
Good advice from garner, but I would ask, how much do you exercise the dog? Springers are hunting dogs, first and formost, and need quite a bit of good, strenuous exercise. I would recommend, based my experience with our own Springer, at least 30 minutes of good heartbeat raising walks a day. One hour is far better. I think you'll notice a difference in his/her demeanor. I even try leashing him during a bicycle ride to assure the dog gets somewhat winded...Best of luck!
When does he pant? Is it really all the time? During the day when it's hot? After exercise? At night?
In case he's hot, make sure he has access to plenty of fresh water and try and keep him in a cool place.
I'd be worried in case it was something else - some heart conditions can make dogs pant more than usual. If it's not just the heat, best take him to the vet just to be sure.