What was found
SEA - DURING CLIMB THROUGH 19K FEET, FUSELAGE DOOR WARNING LIGHT CAME ON. ON DESCENT THROUGH 14K FEET, CABIN PRESSURIZATION WAS LOST. CABIN PRESSURE WENT FROM 4 PSI TO O PSI IN A FEW SECONDS. EMERGENCY CHECKLISTS WERE PERFORMED AND THE LANDING WAS UNEVENTFUL. MAINTENANCE INSPECTED THE AIRCRAFT AND REPLACED THE REAR CARGO DOOR "PRESS TO RELEASE" BUTTON AND ATTACHED THE SPRING ON THE DOOR LATCHING MECHANISM. OPERATIONAL CHECK WAS GOOD AND THE AIRCRAFT WAS RETURNED TO SERVICE.