The heart of Frederic Chopin, pickled in a jar of alcohol and then encased in a stone pillar in Holy Cross Church in Warsaw, shows the Polish composer died from complications of tuberculosis, according to an early version of an article published by the American Journal of Medicine.

According to the article, which is to be published in its final form in February, the researchers found Chopin’s heart “submerged in an amber-brown liquid,” thought to be cognac, which was often used for tissue preservation.

The researchers did not open the jar, but they could see that Chopin’s heart was “massively enlarged and floppy,” they wrote in the article. It was also covered in a white substance that gave it a “frosted” appearance, leading the researchers to conclude that Chopin had suffered from pericarditis, an inflammation of tissue around the heart that was likely the result of tuberculosis. Previous theories held that he may have died from cystic fibrosis.

The heart has a long and contentious history. Chopin, who died in Paris in 1849 at the age of 39, feared being buried alive, and asked that his body be cut open before burial and his heart sent to Warsaw. Accordingly, his heart was cut out, sealed in a crystal jar and smuggled past Russian authorities into what is now Poland.

During the Warsaw Uprising in 1944, the occupying German forces, anxious about Chopin’s status as a Polish national icon, suppressed performances of his music. His heart was removed from the church and kept at the headquarters of the SS commander Erich von dem Bach-Zelewski. After the war, it was returned to the church and interred in a pillar inscribed with a verse from Matthew: “For where your treasure is, there your heart will be also.”

On an April evening in 2014, a small group that included Polish scientists, church officials and members of the Chopin Institute disinterred the jar and examined its contents in secret.

Michal Witt, the lead researcher on a team of Polish scientists who worked on the article, said it was important to understand the heart as a symbol of Polish national identity: “For Poles, this piece of his body which is present still in Poland is of special emotional value.”