What was found
DFW - FLT 341 - EN ROUTE GDL-DFW, AT 37,000 FEET, PRESSURE FLOW LIGHT ILLUMINATED. CABIN CLIMBED AT 300 FEET PER MINUTE. PERFORMED ABNORMAL PROCEDURE AND CABIN RATE WENT TO ZERO, THEN BOTH PACKS FLOWS WENT TO ZERO AND CABIN BEGAN CLIMBING RAPIDLY. MAXIMUM CABIN ALTITUDE REACHED WAS 1,200 FEET. CABIN MASKS DEPLOYED AS PART OF EMERGENCY DESCENT PROCEDURE. LANDED DFW WITHOUT INCIDENT. REPLACED PRESSURE REGULATOR VALVE ON LEFT SIDE, OFF 13TH STAGE BLEED AIR. SYSTEM GROUND CHECKED NORMAL OPERATION. (M)