Greyhound

Not a warm-climate breed by history, but built to shed heat: a very short coat, little body fat and a long, narrow muzzle. Retired racers are widely available for adoption across the US and are calm at home, needing less exercise than their speed suggests. The danger is the sprint itself; a flat-out chase on a hot afternoon can tip a Greyhound into heatstroke, so save running for the cool hours.