Wikipedia
Herzgruft
The Herzgruft is a burial chamber that protects 54 urns containing the hearts of members of the House of Habsburg. The crypt is located behind the Loreto Chapel in the Augustinian Church within the Hofburg Palace complex in Vienna, Austria.
The first heart, belonging to King Ferdinand IV, was placed in the Augustinian Church on 10 July 1654, according to his wishes. The last heart, belonging to Archduke Franz Karl of Austria, was placed in the crypt on 8 March 1878. The bodies of all but three of the hearts are in the Imperial Crypt a few blocks away.