The 'baby' was wrapped up in a blanket with only the top of its forehead peeping out. One concerned officer saw the 'child's' head was discoloured and was worried it was ill.
Despite trying to find the owner of the car, which was parked outside Russell Hall Hospital in Dudley, no one came forward.
With the clock ticking, officers broke a window to rescue the tot from the vehicle. But when they took the blanket off the abandoned little one, they saw it was just a very realistic-looking doll.
Chief Insp Phil Dolby told The Daily Mirror: "With time passing, the officers were left with no option but to break a small window to investigate further.
"We think they did the right thing when faced with what they genuinely believed was a baby, alone and critically ill in a locked car in the hospital car park."
It was reported that police apologised to the car owner, and agreed to cover the cost of fixing the window.
He added: "She will hopefully agree if it had been a baby in distress and had they not acted in the way they did, they would be subject of this scrutiny for all the wrong reasons."
For exclusive competitions and amazing prizes visit Reveal's Facebook page NOW!