"My Spanish isn't very good, but I could see it was a Christmas list," he told The Washington Post in a phone interview Friday.
Heiss was charmed. He suspected that a child had tried to send Santa Claus a Christmas wish list by balloon, something he used to do himself when he was a kid. Nobody had ever returned the letters Heiss had sent aloft - but he wondered whether he couldn't find the girl who had sent this one.
It would be difficult, but Heiss had a few clues. About 20 miles to the southwest, just across the border, was the city of Nogales, Mexico, with a population of about a quarter-million people.
"Based on the prevailing wind, I was pretty doggone sure that's where it came from," he said.
Heiss brought the note home to his wife, who is fluent in Spanish and helped him translate the list. They determined that Dayami, probably a girl, had asked for "Enchantimals," clothes, art supplies and slime, among other things.
Heiss then posted about his quest on Facebook, attaching photos, hoping some of his friends in Nogales might know the girl's family.
A few days passed, with no leads; Heiss worried that time was running out before Christmas. On Wednesday, he decided to send a private Facebook message to Radio XENY, an AM radio station based in Nogales.
To his surprise, someone from the station called him back right away. Heiss' wife helped explain the situation to Radio XENY host Cesar Barron, who talked about the quest to find Dayami on air and posted about it on the station's Facebook page.
On Thursday morning, Heiss awoke to another message from Radio XENY: They had located Dayami, an 8-year-old girl, and her family, who indeed lived in Nogales. Would they be willing to arrange a get-together at the radio station?
"It just changed my entire day," Heiss said. "Instead of going back to my office in Bisbee, I went with my wife to Walmart."
They bought just about everything on Dayami's list, except for an "Enchantimals" doll and an "Enchantimals" dollhouse (both were sold out). They also bought a few other toys for good measure, since they had learned that Dayami had a younger sister, 4-year-old Ximena.
Then the Heisses drove for 45 minutes, crossing the border into Nogales. They arrived at the Radio XENY offices with presents by the armload - and finally met two very excited little girls.
Their parents explained to the Heisses that Dayami had been writing a letter to Santa and sending it by balloon for years, but this was the first year anyone had found their note.
"Their eyes were wide open with wonder," Heiss said of the two sisters' reactions. "Like 'Oh my gosh, this really did work!' "
Heiss and his wife told them they were "ayundantes de Santa," or Santa's helpers.
"It was a beautiful, beautiful experience," Heiss said.
He paused.
"Quite healing for us," he added.
Heiss, 60, has lived in southeastern Arizona for more than three decades and now splits his time between Patagonia and the city of Bisbee. Nine years ago, he and his wife lost their only child, a son. They have no grandchildren.
"Being around children at Christmastime has been absent in our lives," Heiss said. "It's been kind of a gaping hole in our Christmas experience."
He has since reflected on what a "miracle" it was that he spotted the balloon at all, let alone was able to locate Dayami and her family.
"We now have friends for life," Heiss said. "And, for a day, that border fence with its concertina wire melted away."
