105 It is therefore essential, at this point, in a doctrine of such importance and requiring such prudence that each one constantly hold that the truth of the natural symbol by which the physical Heart of Jesus is related to the Person of the Word, entirely depends upon the fundamental truth of the hypostatic union. Should anyone declare this to be untrue he would be reviving false opinions, more than once condemned by the Church, for they are opposed to the oneness of the Person of Christ even though the two natures are each complete and distinct.
Source: Haurietis Aquas (Vatican.va)