Italian summers, and July–August in particular, regularly push into the high 30s°C in cities, and the risk starts before the air even feels unbearable to a person — pavement and cobblestones can burn paw pads well before that point, especially in the early afternoon. Walking a pet in the early morning or after sunset, rather than midday, sidesteps most of the risk entirely.
The rule that can't be repeated enough: never leave a pet alone in a parked car. Cabin temperatures climb dangerously fast even with a window cracked open, often within minutes rather than the longer timeframe people tend to assume. Early signs of heatstroke worth watching for include heavy or unusually rapid panting, excessive drooling, and sudden lethargy or wobbliness — if any appear, get the pet to shade and cool (not ice-cold) water immediately, and to a vet as quickly as possible.