"I start Friday morning on the 17th at 3 a.m.," Heston said. "I will run through the day, into the night, and I will finish in 27 hours. I have a finish time by 6:30 Saturday, right before the National Anthem of the El Tour de Tucson."
Heston has been running ultra marathons for years, but has never gone further than about 62 miles.
Over the last nine months, he's logged 1,400 miles to get ready.
"Physically I'm there," he said. "Mentally, it's 40 miles further. One foot in front of the other for 24 hours."
His goal is to raise $15,000 for the Community Food Bank of Southern Arizona.
With less than a week to go, he is just over two-thirds of the way to the goal.
"We're hoping to reach the $15,000 mark," he said. "With some giving people in the Tucson community, we can get there."