The Texas Department of Public Safety says the accident happened late Sunday afternoon in Waco.
DPS says the ambulance overturned during wet conditions on the road. The National Weather Service says the area had rain on Sunday.
KWTX-TV reports the ambulance was transporting a patient who had suffered a heart attack. A paramedic and two other emergency medical officials were also on board.
All four were transported to a Waco hospital.
A spokesman for Hillcrest Baptist Medical Center said Monday that the cardiac patient had been admitted. Further details were not immediately available on that patient or the three injured medical personnel.