What is wrong with my cat?

I have a 10 year old cat who I love so much. He is the friendliest most affectionate animal I have ever been around ( i swear by this) anyway I am very worried about him. It all started with him coughing and when he coughs he stretches his neck out and heeves. We have taken him to the vet who though either asthma or cardiomyopathy. He figured it was the cardiomyopathy and the coughing is from that however I have noticed that if I open a window to let the cold air in my cat stops coughing automatically.

It is also a dry cough and from doing some research on this myopathy causes a wet cough and in fact rarely causes coughing at all. His appetite is fantastic and he is always happy it seems. I have researched some cats on youtube with asthma and it looks and sounds EXACTLY the same. can my vet be wrong? My cat is on a heart medicine that isnt helping and we are even giving my cat coQ10 for pets. I wonder if we tried an pet iinhaler that the vet is wrong. Of course I wish the vet was wrong Id rather my cat have asthma then a heart problem but I am not just saying this cause its wishful thinking. I truly believe my cat has asthma. Anyone have experience about this? I am really worried about my cat, I love him so much. Anyone know what to do when he is coughing how to make him feel better? Home remedies for asthma? Perhaps a test to see if it is asthma or a heart problem.