After a seemingly endless rainy season (never really cold and never really warm) summer seemed to arrive in mid-summer's day. This morning my flat is already 28C with no heating of any kind and no sunny windows.
In hot weather your blood vessels dilate and particularly if you are on beta blockers, ACE inhibitors or any other BP medication. Symptoms of this include light headiness, dizziness, nausea, and even vertigo and vomiting. If affected you should not drive even on short local trips as you can as easily seriously injure and kill someone 100yds away as a 100 miles away.
Also if you are on a fluid restriction contact your heart insufficiency nurse (I do not say heart failure as it is not a failure) or other medical professional as you may be allowed a temporary fluid intake increase for the duration of hot weather. I personally perspire bucket loads during hot weather or physiotherapy.
There is more on the Heart and Hot Weather here: