On August 18th, 1996, Father Alejandro Pezet performed Holy Mass at the Church of Santa Maria y Caballito Almagro in Buenos Aires, Argentina. After finishing Holy Communion, a parishioner came to the priest telling him that she had found a discarded host on a candle holder in the back of the church. Following normal practice, he placed it into a glass of water and put it inside of the tabernacle so that it would naturally dissolve.
On August 26th, he opened the tabernacle to ensure it had dissolved. Upon inspecting the glass he quickly realized the host had instead transformed into a large piece of bloody tissue. Father Pezet immediately called bishop Bergoglio (now Pope Francis) and the archbishop told him to have it professionally photographed. A photographer came on September 6th and the host was placed back inside the tabernacle without publicizing it.
For three years it stayed there, never decomposing. On October 5th, 1999, Cardinal Bergoglio ordered the host to be scientifically examined. Doctor Ricardo Gomez took a sample in the presence of the Cardinal's representatives and had it sent to New York for analysis. Intentionally to not spoil the investigation and to not bias the results, the sample was sent without a description of it's origin.
Doctor Fredric Zugibe, a famous cardiologist and forensic pathologist who studied the sample in New York testified:
“The analyzed material is a fragment of the heart muscle found in the wall of the left ventricle close to the valves. This muscle is responsible for the contraction of the heart. It should be borne in mind that the left cardiac ventricle pumps blood to all parts of the body. The heart muscle is in an inflammatory condition and contains a large number of white blood cells. This indicates that the heart was alive at the time the sample was taken. It is my contention that the heart was alive, since white blood cells die outside a living organism. They require a living organism to sustain them. Thus, their presence indicates that the heart was alive when the sample was taken. What is more, these white blood cells had penetrated the tissue, which further indicates that the heart had been under severe stress, as if the owner had been beaten severely about the chest.”
This testimony describes the sample having a large number of white blood cells present, indicating the tissue would have had to been removed from a heart that was fresh and still in the process of pumping. This alone ruled out several accusations of fraud, as the sample would have had to been gathered from a live human being, not a cadaver. Furthermore, the tissue should have significantly decomposed by this time.