Heather Locklear - transported to a hospital and placed in ICU

TMZ has obtained the 911 call placed January 12 by Heather Locklear's sister ... the tape is heavily redacted because of patient confidentiality, but TMZ has learned the nature of the emergency.

Law enforcement sources tell TMZ ... Heather's sister told the dispatcher Heather was having intense stomach pains and was in severe distress.  When paramedics arrived they performed some tests and quickly decided her condition was so serious Heather needed to be transported to a hospital and placed in ICU immediately.

TMZ broke the story ... paramedics examined Heather after her sister made the emergency call, and determined Heather needed to be hospitalized after she had taken a dangerous combination of prescription drugs and alcohol.

It's her second drug-related emergency in the last couple years -- Heather was hospitalized back in 2008 for what the 911 operator described as a "suicide attempt" ... after her doctor became concerned Heather may have OD'd on prescription pills. It turned out to be a false alarm.