The UFC confirmed the news in a statement, saying the Brazilian fighter was found unresponsive on the morning of Monday, 3 August.
“This morning, Monday, August 3rd, our beloved fighter and exemplary flyweight, Allan Nascimento, was found unresponsive after suffering an apparent heart attack in his sleep,” the organisation said. “Despite the efforts of the responding medical team, he was pronounced deceased at the scene.
“Our thoughts and deepest condolences are with Allan’s family, friends, teammates, and loved ones during this incredibly difficult time.”
Nascimento, a Sao Paulo resident, leaves behind a wife and two children.
His last fight came in June, when he suffered a split-decision defeat to Mitch Raposo. The flyweight competed out of the renowned Chute Boxe gym in Brazil and held a UFC record of four wins and two defeats, with an overall professional MMA record of 22 wins and seven losses.
Chute Boxe paid tribute to the fighter, describing him as a warrior, friend, dedicated competitor and extraordinary human being.
“Allan inspired on and off the mats with his determination, humility, respect and fighting spirit,” the gym said. “Your presence will be missed immeasurably. Rest in peace Allan, your name, your story and your legacy will live forever.”