Suffolk Fire & Rescue units detected carbon monoxide inside the store with their gas meters.
The store was evacuated at 9:44 a.m. and remained closed until 1:05 p.m.
There are no reports of any injuries or patients associated with the incident.
Virginia Natural Gas responded and secured the gas lines to the building as a precautionary measure.
The HVAC units at the building are remotely controlled at a Walmart facility out of state and regional maintenance personnel were contacted by local Walmart officials to respond to the store to isolate the cause of the detection of carbon monoxide and the odor of gas.
The personnel were able to isolate the problem to rooftop HVAC units.