Welcome to Santa Fe and to Scoop, Patti. Your little Chihuahua looks almost like our little boy Rico who died 11 days ago. You can see him in my profile here at Scoop.
I have never seen a flea on my dogs nor worried about heartworm here, but then I tend to be on the cautious side before I dump any kind of medications into my animal children. I'll be curious to see what other responses you get.