Summer heat means being extra careful with your pets, especially flat faced little dogs like Shitzus. They tend to heat up very quickly and, because of their tiny flat noses, can have a very difficult time breathing.
Although these little guys love to be outside, you need to have a cool environment available to them when they start to heat up, particularly on days with high humidity.
Keep an eye on them and bring them into an air conditioned car or house immediately if you hear them wheezing or having trouble breathing...that is a danger sign of overheating. Also, keep an eye on how much they are panting. Regular panting is normal and is how they cool themselves. However, the panting should slow down or stop altogether when they have cooled themselves. If this is not happening, again, bring them into a cool environment. Also, make sure they always have a good supply of fresh, clean, cold water.
I think it goes without saying (but I'll say it anyway) - NEVER EVER leave them in a car alone with the windows closed in warm, sunny weather. Don't even leave them in the car with the windows open on a hot sunny day - keep them at home.
I also like to give the little guys a cool bath on hot, humid days. It's probably the one time they don't hate me for doing this!