Gasping for breath because its "too hot"

Some good advice here:
1/ Telephone appointment with the doctor if he won't go in.
2/ Buy a pulse oximeter to check his blood oxygen levels. Something you could do before and after exercise, or indeed any time. Loads on Amazon.
3/ Check hiatus hernia or other possible causes.

Ex Dancer , I have no experience of the oxygen canisters you refer to, but my instinct would be to stay clear of them . You have obviously tried to get your DH back to the GP and I recognize he has had lots of investigative procedures, however he is clearly not well. If he won't listen to you, have you AC that would speak to him or failing that a good friend who would try and persuade him to visit his GP? I do hope you make progress with this matter.

We're a bit off topic, I was actually asking if anyone had tried using those little canisters of pure oxygen you can buy. They are like a very large fly-spray and come with a mask, and you put the mask over your nose and mouth and take a breath.
They sell them on places like EBay and Amazon.
I've tried to copy and paste an image but must be doing something wrong, I'm not very competent with IT.

Just remembered, anemia also causes shortness of breath. Anemia contributed to my recent problems regarding breathlessness. Since treatment I am much better.

My first thought was is it hayfever, I’m always shorter of breath when the sun is out in May and June because of it, it definitely affects my airways. I use Allevia, which used to be prescription only but you can now get over the counter.

Is there a problem with his temperature regulation system? The body should adjust itself to the surrounding temperature, with sweating or shivering as appropriate. Perhaps he just needs to find a way to cool down when it's hot.

Could he be persuaded to do a telephone appointment? At least things could be put in place after that. He doesn’t necessarily need to actually see the GP again if he doesn’t want to.

Hmm ... very difficult.
?? Asthma caused by pollen count??
?? Try antihistamine like cetirizine.
You can either persuade him to try drs again or wait until he collapses and ring for an ambulance.
Or you could try ringing 111 for advice.
The other thing I find useful is a little oxygen monitor to see if his 02 Sat's are above 95%
They are not dear but very useful.
Especially with "Covid around.
Men can be so difficult.

I forgot to say he's now flatly refusing to go back to the doctor's because it's a waste of time. I didn't want to write a long screed that no-one bothered to read, and omitted that important fact.
Believe me, if I could get him to the surgery I would have done it months ago.
He's had ECGs, echocardiogram, the procedure where they stop and start your heart (I forget the name) three times, plus other strange procedures involving isotopes - you name it, he's had it.
But not hiatus hernia Aldom, thank you for that.
I wonder if I can persuade him back to the surgery for one more 'try' ....... ?
His gp won't discuss it with me of course , I have tried.

Hiatus hernia can cause shortness of breath. Cardiology have given me a thorough investigation, only to find my breathlessness is caused by my hiatus hernia. Perhaps your husband could ask his GP to consider investigating this area.

Definitely see the GP. It doesn’t need to be tomorrow, you can make a appointment for when you are able to book one. At our GPS we can book an appointment online about two weeks in advance. Do that tomorrow and avoid any exercise that leaves him struggling in the meantime.
Good luck.

Off to the drs.

Has he had long covid?

Get him to the doctors asap. That is not right. He needs a heart check.