I believe in my heart and openly profess that the bread and wine placed upon the altar are, by the mystery of the sacred prayer and the words of the Redeemer, substantially changed into the true and life-giving flesh and blood of Jesus Christ our Lord, and that after the consecration there is present the true body of Christ which was born of the Virgin and offered up for the salvation of the world, being hung on the cross and now sits at the right hand of the Father, and there is present the true blood of Christ which flowed from His side. They are present not only by means of a sign and of the efficacy of the sacrament, but also in the very reality and truth of their nature and substance (Pope Gregory VII - Council of Rome, February 11,1079)