A 41-year-old Belgian man was among the dead after a tree fell on his tent at a Rainbow Gathering counter-cultural summer camp in the Tramontina valley in the northeastern region of Friuli.
Another tree, uprooted by powerful winds, fell on a festival at Marzia in the Dolomites, killing another man.
A hiker was fatally struck by lightening on a path up a mountain in the same area, the Marmolada.
The weather-related deaths follow a storm-triggered mudslide on Saturday which swept a woman to her death on the outskirts of the ski resort of Cortina d'Ampezzo.
On Thursday, two pensioners died in central and southern Italy after being caught up in wildfires triggered by the heatwave and weeks of severe drought.
Rainfall in July was nearly 50 percent lower across Italy than is normal and peak temperatures have been hitting at least 40C (104 Farenheit) across nearly the entire country for almost a week.
The highs are not unusual but the duration and widespread nature of the heatwave is, weather experts say.