High HR due to heat?

My HR during power zone 2 is usually 135 to 150 bpm. It does not go over 150bpm unless I mix in some tempo and my max is around 203bpm.

Today’s temperature was around 36ºC(humidex) and my HR during zone 2 was > 145bpm. How much does heat affect performance? The weather has been pretty cold during the first half of June. It didn’t go above 17ºC for the most part. Today is the first heatwave of the year and will my body get used to the heat so that my HR will be normal like before?

edit: my sleep was also interrupted. Could that also be the cause? I also got dehydrated and had to stop 2 times for water

Yes, heat will affect your HR. Lack of sleep and dehydration can to, but its fairly normal that your HR is higher when it’s hot.

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it was too high. It was mostly in the 150s… I guess I messed up my hydration as I rode for ~40 kms without water

There is a lot of good info on HR decoupling here. Dehydration definitely has a big impact and riding 40km with no water in 36C heat will do it!