The heat warning issued for Waterloo Region and most of southern Ontario has continued into Saturday.
Daytime temperatures are expected to peak in the mid 30's, with humidex values in the low 40's.
Little relief is expected Saturday night as temperatures will only fall to the mid 20's with humidex values remaining near 30.
A cooler and less humid air mass is expected to arrive on Sunday.
Environment Canada warns that extreme heat affects everyone, but the risk are greatest for young children, pregnant women, older adults and people with chronic illnesses.
Those working or exercising outdoors should also do so with caution.
Relief is expected to come Sunday with the arrival of a weak cold front.
