No Heartgard/Flea Treatment - More Stamina?

We've had some REALLY hot days this month. I thought for sure Gracie wouldn't be up to playing outside, but she wanted to go out every day --- even when the outside temperature was at least 90 degrees F and the sun was blazing. She looked so glum when I told her we couldn't play outside, I HAD to give her five minutes of "Tennis Ball Fetch." Then she'd take a rest in the shade under the trees, take a drink of water and come back for more. I refused to keep her outside playing in that heat for longer than 10 minutes.

During past summers, Gracie would take playtime a lot easier on hot days. Since she's 12 this year I thought she'd noticeably slow down. I believe a homemade diet can improve and maintain a dog's health. Yet at some point in life, old age will inevitably get the upper hand. Apparently, that's not happening to Gracie yet.

Why, though, does she seem to have more stamina this summer than she did last summer and in year's past? It's really puzzled me. Then I realized this is the first summer, in all the years I've had Gracie, that I've not given her Heartgard preventive. It's also probably the first summer I've never given her any topical flea and tick treatment (I can't remember, 100 percent, about the flea and trick treatment but I'm pretty sure she's had at least one treatment every summer).

I know Heartgard preventive and topical flea and tick control are very helpful under many circumstances. Yet I suspect withholding these preventive meds from my dog this year is the reason she seems to have so much more stamina this summer, even though she's now 12.

Yet even a very energetic dog will seek shade during a game of fetch on a hot summer day. Below is a short video clip of Gracie doing just that when we played outside recently.