Randy Travis -- Fitted with 'World's Smallest Heart Pump'

Randy Travis has been outfitted with a device that's considered the "world's smallest heart pump" ... TMZ has learned.

Travis' publicist, Kirt Webster, tells TMZ ... the singer did NOT undergo heart surgery, contrary to reports, but did have an Impella peripheral left ventrical assist device placed in his heart for "stabilization while transferring hospitals."

According to the company that makes the Impella device, the pump is commonly inserted through a "standard catheterization procedure" -- in which the doctor inserts a catheter into an artery in either the arm, groin or neck and send it all the way to the heart.

We're told the device is considered the world's smallest heart pump -- the same size as a coffee stirrer and smaller in diameter than a pencil.

FYI -- according to the Mayo Clinic, a ventricular assist device (VAD) is "an implantable mechanical pump that helps pump blood from the lower chambers of your heart (the ventricles) to the rest of your body."

Travis' rep insists the procedure is minimally invasive -- and therefore NOT considered heart surgery.

Travis has also issued a statement ... saying, "We are very thankful to the fans for their love and support during this time."

We're told cards and well wishes can be sent to:
Randy Travis
266 Blanks Road
Tioga, Texas 76271