"Doctor" Jon Basso, the owner of the restaurant and not an actual medical doctor, said he originally thought Saturday's incident was a joke when one of his "nurses" told him a patient was experiencing chest pains, KVUU-TV, Las Vegas, reported Wednesday.
Basso, who opened the restaurant in October, said the customer was eating a concoction known as the Triple Bypass burger when he began experiencing chest pains.
"The gentleman could barely talk," Basso said. "He was sweating, suffering. Anyone with an ounce of compassion would've felt for him."
The man was taken to a hospital by paramedics. Basso, who declined to identify the man, said he is recovering.
The Heart Attack Grill is known for glorifying unhealthy eating habits, with several menu items exceeding 8,000 calories.