Quality Control Cofounder Pierre 'P' Thomas Improving After Heart Attack

Quality Control Music cofounder Pierre "P" Thomas -- who helped build the careers of stars including Migos, Lil Baby and City Girls -- is still recovering in the hospital after suffering a heart attack ... but we're told his health is improving.

A source familiar with the situation tells TMZ ... P is still recovering at a Las Vegas hospital, where his health continues to improve.

As we reported ... P was hospitalized Friday after suffering a heart attack and was being treated in the ICU.

Quality Control Music previously told us P was receiving medical care after his hospitalization ... while asking fans to keep him in their prayers.

P cofounded Quality Control Music with Kevin "Coach K" Lee back in 2013 ... helping build the label into a hip-hop powerhouse.