Merrillville police say they were notified about a possible animal distress in the 5500-block of Jackson Street around 2:20 p.m.
When officers arrived, they found the dog lying motionless under a swing set in a yard.
The dog was tethered and could not get out of the sunlight or reach a bowl of water. The temperature was over 90 degrees.
Police said the dog was breathing slowly and appeared to be suffering from severe heat-related distress. They tried cool the dog with water and get it to drink, but it was unable to.
Officers took the dog to a nearby animal hospital for emergency treatment, but it did not survive.