WELCOME! to the forum.!
You could try turning your humidity up a notch and seeif that will help but hang in there for more suggestions and best of luck to you.
I only have my own issues to use for knowledge. At times I 'hiss' at night, and those are the times that my mouth is very dry, cheeks stuck to teeth, tongue stuck to the roof of my mouth - that or drooling very badly - no idea why one vs the other - but my wife does confirm my 'hissing'. For me, a switch from CPAP to a BI-PAP helped with this issue greatly - but, I've read that newer CPAP machines have a way to lower your pressure on exhale? If so, perhaps that might help??
I do not know if you use a high pressure, or are brand new to CPAP, or recently had a pressure change? If fairly new to CPAP, perhaps something as simple as time my help (your body getting used to the whole thing).
As for the heart issue, I have no thoughts at all - other than making your heart DR or PCP aware of what is going on here.
*I* am not a DOCTOR or any type of Health Care Professional. My thoughts/suggestions/ideas are strictly only my opinions.
"Only two defining forces have ever offered to die for you. Jesus Christ and the American Soldier. One died for your Soul, the other for your Freedom."
Dry mouth is a sign of mouth breathing, If air escape thru the mouth, reduces the effectiveness of the therapy
Its important to keep mouth closed while using a nasal mask
Chinstrap helps keeps mouth closed and minimize mouth leaks
FYI ... Activa LT cushion fit SoftGel mask frame, I find it lighter and easier to maintain a seal but of course everyone is different