If you ever suspect your dog having problems due to the heat or ingesting something, get him or to the vet immediately. Summertime hazards can be found in many places. This is not a complete list, but some of the more common issues. You can also visit the ASPCA site for up-to-date information on a variety of issues.
Overheating. Dogs can overheat on normal walks or even faster in the the car. Take lots of water with you, avoid the heat of day, take shorter walks, and NEVER leave a dog in a car alone, even with the windows open. A car can heat up to a lethal temperature in minutes. Just don't take a chance.
Theft. Dogs can get taken for medical experiments, dog fighting, or for their companionship. There has been a rash of small dogs getting taken out of cars in Chicago. The thieves smash the windows and take the dogs. Some police think that the thieves might look for reward signs and return the dog to the rightful guardian to claim the reward. Evil. Dogs also can get taken when tied up outside of stores or coffee shops or out of backyards. Be careful.
Ingesting Antifreeze. This is the main reason I never let my dogs drink out of puddles. I don't want them to get in the habit of doing so. Even a small amount of antifreeze can kill a dog, and to make it worse, the sweet taste attracts dogs.
Ingesting chocolate. There is a lot of great information out there about the toxicities in different types of chocolate. Dark chocolate and baker's chocolate is the most dangerous, but it is a good idea to keep all chocolate away from your dog. Here is an article about the dangers of chocolate at About.com.
Ticks. Ticks have got to be the nastiest looking creature out there. Besides the skin irritations they can cause, they can also carry Lyme Disease. Make sure you check your dog thoroughly after every romp in a potentially tick-infested area. Learn more about Ticks at this informative website
Giardia. Dogs can get this parasite from the waste of other dogs. So, if you are out more with your dog in the summer, make sure you are in a clean area. Here is an article about Giardia. As you can see, it is a complicated topic.
There are a lot more dangers for dogs out there, if you have more that you would like to talk about add a comment to this post.
Have a safe summer.