Video showed the lawyers ransacking wards at the cardiac hospital, beating up staff and smashing equipment.
As panic spread, doctors and paramedics hid, leaving patients unattended, including those in a critical state.
Riot police fired tear gas to disperse the lawyers and more than 20 arrests were made. It took more than two hours to restore order, officials said.
The lawyers had been protesting over the alleged mistreatment of some of their colleagues by hospital staff last month.
But the final trigger for the violence appears to have been a video posted on social media by a doctor on Tuesday night in which he poked fun at the lawyers.
According to hospital administrators, more than 200 lawyers wielding sticks stormed Lahore's Punjab Institute of Cardiology (PIC) at midday on Wednesday.
Hospital officials said the lawyers forced their way past security and split into groups, attacking various departments and wards.
Video footage shared on social media showed lawyers - in suits and ties - smashing medical equipment and windows, and beating up staff and officials including Punjab information minister Fayazul Hasan Chauhan who had arrived on the scene to try to restore calm.