Cat Panting

We have a two year old cat that we adopted some time ago.
A few days ago I purchased a laser light toy for her.
We have 3 other inside cats too, and although they like to chase it around, our two year old was super excited about it.
Just the click of activating it gets her extremely excited, and she also does that nervous type chattery mouth thing that cats do as they watch a bird or squirrel through the window.
Well anyway after getting it out for her first time to play with it, she was extremely excited, and chased it from room to room. After about ten minutes I began to notice a strange noise. It was her panting.
I quit put it up and after about 3 to 5 minutes and she calmed down and the panting stopped.
We still continue to let her play with it, but other than the nervous chattery mouth thing that she does that's about it, as it appears that she is getting use to it.
We've only seen her do the panting on her first encounter, and that's it.
To date I've never seen a cat get so excited about toy, and she still does, just not to the point of panting.
The other day on a visit to our vet for supplies I told him about this.
He said that this behavior is 100% of the time a medical issue with an underlying cause like a heart problem.
All my research seems to indicate that this is not true.
Should I really be concerned about this one time event, and the circumstances that brought it on?
Thanks in advance for any thoughts!

No, definitely not true.
Cats will definitely pant when overheated, it just takes more than it does for a dog.
Rigorous exercise, coupled with ambient temperature can cause a cat to pant.
While I do agree that panting can also be a sign of heart conditions, this is not usually the case.

Your vet, however, is probably not lying, I'm sure that from his perspective this is true, afteral, people take sick cats to see him.

Do have him check her heart at her next visit, just to be certain, but mostly, limit the time spent with the laser pointer if she gets that excited about it.

Not to worry. I play interactives with my cats every night. And they will pant if they get so overly energetic. Also, if the temps are warmer combined with playing most cats will pant. Perla will just plop down and pant for a few minutes and then go again. They all do it occasionally depending how excited they are into the play session.

Now, if you cat is distress panting and has not been playing, this is a sign of medical emergency