The heart of Christianity is the Lord Jesus Christ Himself and His blood and body sacrifice for our sins--not St.Peter's Basilica.
Yes, in The Holy Sacrifice of The Mass and in the divine instruction given to Peter, the keys to the Kingdom of Heaven, his apostles and their successors to teach one faith, one truth, and as part of one church, and the gates of hell shall not prevail against it.
St. Peter’s church is the “heart of Christianity” to over 1 billion folks, who all BELIEVE in Jesus. Is is built over the tomb of Jesus’ Apostle, Peter. Can you say that of any other church?