Doctors and patients did double-takes when two mini horses ambled down the long corridors of a Chicago hospital and into patients' rooms.

The dog-sized horses - named Mystery and Lunar - are from the Mane in Heaven animal therapy team based near the city.

Their first visit inside a hospital was a recent trip to Rush University Medical Centre and more are planned.

Studies suggest animal-assisted therapy using dogs may reduce pain and blood pressure, and decrease stress in hospitalised children but much of it is based on patient reports.

"They're so nice and they don't judge and they're so sweet," said epilepsy patient Emily Pietsch, 17.