Glacier National Park staff say traffic on Going to the Sun Road was restricted for three hours on Monday while staff responded to a medical emergency.
A park release says at 3 PM on Monday, Sept. 2, rangers responded to help an unconscious man in a vehicle just west of Lake McDonald Lodge.
First responders administered CPR but the man died on the scene.
The man is listed as a 64-year-old from Whitefish. He's believed to have died of a heart attack.
The park doesn't typically release statements for deaths from natural causes, but a number of people witnessed this particular incident.
Park rangers, Three Rivers Ambulance, A.L.E.R.T. Air ambulance and medically qualified bystanders assisted with the response.