Get Your Dog Care Questions Answered by Experts
I am sorry to hear you are worried about Bruno. I am a veterinarian and will do my best to help.
Vomiting blood can happen with many medical conditions. I would not be thinking this was a heat stroke. What is his rectal temperature? Has he been running hard on a hot day? If you check his gums, are they a normal pink color? He could be nauseous, foaming, and vomiting for many reasons: something he ate, an infection, etc.
Unless it is a hot day, and he has a rectal temperature over 104, this may not be a heat stroke. Dogs usually get heat strokes from being accidentally locked in cars with the windows up, or from running and playing hard on a hot day without rest or water. If you check his gums, are they pink in color or pale? Can you take his temperature?
If he were mine, I would start by checking his gums, listening to his heart and lungs, and taking his temperature. It could be a heat stroke, but that does not usually happen in young dogs just taking a walk. I wish I could see his gums, feel his pulse, listen to him with a stethosocope!
If he is vomiting blood, I am pretty worried. Can you get him to veterinarian?
Having to stop and rest could be exhaustion, but he seems too young for that. I would be worried about his heart, lungs, digestive tract, or internal bleeding. If his gums look pale, that is concerning to me, a possible sign of shock, internal bleeding, internal illness. I really wound need to examine him to narrow down the possibilities of what is wrong. I hope he is stable until you can get him to a veterinarian.
The only way to check if this is heatstroke is to take his rectal temperature. Usually dogs with heat stroke are over 105, I have seen 108. Normal is 101 to 102. Recovery from heatstroke can be rapid as soon as you cool the dog down, and start IV fluids.