I'm reading The letters of Madame Sevigne (Barnwell's translation), and one of the footnotes says that after her early marriage to the Duc de Rocquelaure, Mme de Roquelaure had fallen in love with the Marquid de Vardes. Her love being unrequited, she died of a broken heart at the age of twenty-one. What is it to die of a broken heart? Is it a euphemism for a specific end?