Thank you for your reply, Hazel!
The vet recommended that Beau take half of a baby aspirin if he is ever in pain. He does get quite sore after running around (which he does every day) but his mobility is a little less in general, i.e. he's hesitant to climb the stairs and jump onto the bed.
Unfortunately, as Beau is living with my parents right now, I'm not sure if they will bring him to a canine cardiologist as long as the primary vet sees no need for it. This is a huge point of argument between us, because I'm more than willing to pay out the nose for all kinds of tests... however, I am a hypochondriac and would probably spend the money unnecessarily, as he does seem to be very healthy.
The more I think about it, the more I realize that he has always been a bit of a huffy breather since he was a puppy. I guess it's just my high anxiety, combined with the fact that I don't see him every day that gets me worrying.
I will keep an eye on it and get him into the vet for another routine checkup within the next few months. If anyone has any other experience with this, it'd be much appreciated, or even opinions on whether or not it could be just arthritis.
Here are a couple pictures of Beau, and one of my Bichon Frise, Oscar!