Excess yawning when under a load - heart problem?

Hello, and thank you so much for this service.  I am a 64yo female in good health.   However, both parents had heart disease.   My father's brother died of a heart attack, and my own brother (1 yr younger) had a mini heart attack.  My problem is that when doing my resistance machines workout I need to take very deep yawns, pretty much after each machine, in order to be able to take a deep breath.   Apparently my breathing becomes very shallow when directly engaging with a machine.  This has been going on for a few years now but seems to be increasing in frequency.   I've noticed that the inability to take a deep breath has also occurred over the past few months even when I'm not under a physical load.   I have mentioned it to my doctor several times over the years but my EKG and an echo cardiogram were fine.  FYI my resting heart rate is low 60's, with low blood pressure and usual body temp of 96-97 degrees.  I do have Hashimoto's which may have something to do with these low ranges (just guessing).   My cholesterol is also good.   I just want to know if my body is trying to tell me something with all this deep yawning.   I don't want to precipitate a heart attack by ignoring these yawns, which is what I have been doing up to now.   Thank you for any clarity you can lend to this situation.

[Cleveland Clinic]

With a normal echocardiogram and a normal ECG the likelihood that these yawn are related to your heart is very low.  I think your heart is working well.  Unfortunately, we have no way of predicting heart attacks in our patients.  It would be nice if we could.  We can only test for significant coronary artery disease which is completely different from a heart attack.  So I would continue to exercise as much as you can but use common sense.  If you develop exertional shortness of breath or chest pain you should seek medical attention.