Cats don't usually pant like dogs and panting can be a sign of heart issues BUT if it is happening after heavy exertion and she is looking alert, not in any distress and her tongue is nice and pink/red when she is panting then I wouldn't be worried. If you are in the slightest bit concerned then off to the vets
When Riley was a few months old I bought them a 'da bird' - it cost around £600 in vets bills as he would go mental playing with it and would stop and pant. Cue vet examination, an X-ray, an ECG, ultrasounds and a blood test - verdict - he was running round like a loon and had worn himself out
I showed the cardiologist a video of him panting (after he had been diagnosed fit as a fiddle, they couldn't get the photobucket link to work so had to wait til I saw him in person to show him it on my phone!) and he said that if he panted after heavy exertion, as long as he was alert, looking around, not in any distress and his tongue was nice and pink then it was nothing to worry about.