An MTA bus driver crashed into an elevated subway pillar in The Bronx when she suffered a possible heart attack Thursday — leaving 12 passengers with minor injuries, cops and sources said.

The 44-year-old Bx21 driver was heading south on Boston Road when the medical episode occurred and she hit the stanchion at the West Farms Road intersection around 8:25 a.m., authorities said. 

She suffered head trauma and was taken to St. Barnabas Hospital, where she was listed in critical but stable condition due to the medical episode, which sources said was possibly a heart attack. 

Twelve passengers suffered minor injuries and were taken to local hospitals, cops said.

No other vehicles or pedestrians were involved in the crash.