Randy Travis Doctors -- Bad Ticker NOT From Drugs or Booze

Randy Travis' heart issues which landed him in the hospital a week ago ... are NOT the result of drug or alcohol abuse, according to his doctors.

Doctors at the Texas hospital where Randy is getting treatment just said -- based on images of Randy's heart -- it's more likely that a family history of cardiomyopathy is to blame for his ongoing heart trouble.

They also said the country music star has been using a ventilator -- but he's improving and they hope he'll be breathing on his own soon.

Randy was airlifted to the hospital on July 8 -- and suffered a stroke last week while getting treatment.