Markle was pictured arriving on an ambulance stretcher in Tijuana, Mexico, on Monday, reported The Sun. TMZ reported he had been transported across the border to a hospital in Chula Vista, California.
"Thomas couldn't actually speak to paramedics, and had to write down his symptoms on a piece of paper," reported TMZ.
The Duchess of Sussex's father wore an oxygen mask to help him breathe and was accompanied by paramedics.
Thomas Markle pulled out of Meghan and Harry's wedding in 2018 after he had a heart attack – and had to undergo surgery to repair the damage.
He was due to walk his daughter down the aisle. Prince Charles performed that duty instead.
Thomas Markle said at the time: "I hate the idea of missing one of the greatest moments in history and walking my daughter down the aisle."
Wootton said Samantha Markle had told him: "My father is recovering in hospital. We ask for privacy for the family, for his health and wellbeing. He just needs peace and rest. Godspeed. We are praying. He just needs some rest. It's a travesty how much he's been tortured and how much he's had to go through thanks to my sister's disregard the past few years. That is unforgivable."