The shrine contains his heart.
From wikipedia: Carlo Acutis lived from 1991 to 2006. He died from leukæmia. He was noted for his cheerfulness, computer skills, and deep devotion to the Eucharist, which became a core theme of his life. Acutis was beatified by Pope Francis on 10 October 2020, two days before the 14th anniversary of his death. On 23 May 2024, Pope Francis recognized a miracle attributed to the intercession of Acutis, clearing the way for him to become the first canonized millennial in the Catholic Church.
en.wikipedia.org/wiki/Carlo_Acutis