Avoid being outside on a very warm and humid day if you are in heart failure. We who have cardiac Amyloidosis do not tolerate temperature extremes without negative consequences.

My morning Starts with light exercises.after a light breakfast a spend the cooler morning hours on my patio reading and listening to cool and calming music.

Since I am 88, I just stay indoors and enjoy the air conditioning. Al

My wife Ruth and I try to get as much exercise as possible. In the heat we will walk our streets at night, usually when the temp drops below 85*. Streets are well lit but our driveways are not. I recently bought Ruth a marvelous LED light from Amazon that clips onto a key-chain--useful when encountering traffic as well as on our dark driveways--if anyone interested I will look up the link--cost for two was in the $10 range. Of course a day-time option is walking a mall or Home Depot or Lowes or .... .
Another option we have is Ruth's stationary recumbent, kind of boring!

Don't get much heat in Britain. Lol.