CHICAGO (CBS) — A passenger died on a flight from Chicago to Mexico City early Tuesday.

Aeroméxico flight 683 took off from O’Hare International Airport around 12:30 a.m., and made an emergency landing in Houston about two hours later, after an elderly passenger became unresponsive in his seat.

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The 88-year-old man was traveling with his grandson, and authorities said it appeared he died of natural causes.

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A doctor was on board the flight, but was it was too late to do anything for the man, who reportedly had a pacemaker and several health issues.

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The man and his grandson had started their trip in California, and were going to visit relatives in Mexico.