A Eucharistic miracle is any miracle involving the Eucharist. Reported Eucharistic miracles can be differentiated from Transubstantiation which is also regarded to as a Eucharistic miracle.
Transubstantiation is the transformation of whole substance of the bread into the body and the transformation of the whole substance of the wine into the blood of Jesus Christ during a Catholic Mass or Orthodox Liturgy while reported Eucharistic miracles usually consist of unexplainable phenomenon such as consecrated Hosts visibly transforming into myocardium tissue, being preserved for extremely long stretches of time, surviving being thrown into fire, bleeding, or even sustaining people for decades.
In the city of Lanciano, Italy, around A.D. 700, a Basilian monk and priest was assigned to celebrate the Eucharistic sacrifice in the Latin Rite in the small Church of St.Legontian. Usually celebrating in the Greek Rite and using leavened bread and having been taught that unleavened bread was invalid matter for the Holy Sacrifice he was disturbed to be constrained to use unleavened bread and had trouble believing that the miracle of transubtantiation would take place with unleavened bread.
During the Mass, when he said the words of consecration, he saw the bread change into live flesh and the wine change into live blood, which coagulated into five globules, irregular and differing in shape and size. Various ecclesiastical investigations have been conducted upon the miracle, and the evidence of the miracle remains in Lanciano to this day.
In 1970-71, Professors from the University of Siena conducted a scientific investigation into the miracle. They concluded that the flesh and blood are human flesh and blood.
The Flesh is a heart complete in its essential structure. The Flesh and the Blood have the same blood type, AB, which is also the same blood type found on the Shroud of Turin and all other Eucharistic Miracles.
The Host-Flesh, which is the same size as the large Host used today in the Latin Church, is fibrous and light brown in color, and becomes rose-colored when lighted from the back. The Blood consists of five coagulated globules and has an earthly color resembling the yellow of ochre.