Short answers, pulled from the story.
Heart-burial is the practice of removing the heart after death and interring it separately from the rest of the body. Examples can be traced to the beginning of the 12th century in medieval Europe, where it was common among the higher ranks of society.
Robert the Bruce's heart is buried at Melrose Abbey in Roxburghshire. He had wished it to rest at the Church of the Holy Sepulchre in Jerusalem; Sir James Douglas set out to fulfill that wish but was killed in battle in Granada, carrying the heart in a silver casket around his neck.
Chopin's heart is sealed within a pillar of the Holy Cross Church on Krakowskie Przedmieście in Warsaw, beneath an epitaph sculpted by Leonard Marconi. After Chopin died in 1849, his sister smuggled the heart to Warsaw in an urn, preserved in alcohol, fulfilling his dying wish to have it returned to his homeland.
Queen Marie of Romania's heart was placed in a jewelry box she had received in 1893 and moved several times due to political upheaval. After being stored at the National Museum of History from 1971 to 2015, it was moved in an official ceremony to Pelişor Castle's Golden Room, where Marie had died.
The practice began for practical reasons: when a person of high rank died far from home, transporting the full body without decay or infection was often impossible, so the heart or entrails were carried home instead. It later evolved into a way to memorialize an individual in multiple locations simultaneously.
Starting in the 13th century, the bishops of Würzburg directed their hearts to the monastery at Ebrach in Germany. About 30 bishops' hearts came to rest there over the centuries, though the tradition was broken by Prince-Bishop Julius Echter von Mespelbrunn, who died in 1617 and chose to have his heart buried at the Neubaukirche.