An 86-year-old died as she went into the sea for a swim in Giulianova, while a 74-year-old man died in the sea at Francavilla a Mare, officials told Ansa.
Another man, aged 64, also died while cycling with a friend in Elice, a town in the province of Pescara.
A heatwave advisory has been issued by Italy's civil protection authority as temperatures are expected to hover around 36 degrees Celsius for the next couple of days. Children, the elderly and the chronically ill are most at risk, officials said.
Over 100 people, mostly elderly, died of heat-related illnesses during the summer of 2015 – Italy's warmest for more than a decade.