TMZ has just found out that Dennis Quaid's newborn twins are fighting for their lives after being inadvertently overdosed at Cedars-Sinai Medical Center in Los Angeles.

“Thomas Boone and Zoe Grace — were accidentally given a massive dose of Heparin, an anti-coagulant. Babies typically get 10 units. Our sources say they were each mistakenly given 10,000 units. The drug is used to flush out IV lines and prevent blood clots.

We're told one dose was given on Sunday morning, another on Sunday evening. We're told a technician stored the Heparin in the wrong place, and when a nurse grabbed the medicine for the babies without looking — it was the wrong dosage. The twins were born to Quaid and wife Kimberly Buffington November 8 via surrogate."