Italy's former president Francesco Cossiga died on Tuesday at a Rome hospital aged 82.
Cossiga was admitted to Rome's Gemelli hospital Aug 9 with cardio-respiratory problems, and his condition turned "drastically" worse overnight, the hospital said.
A heart circulation crisis was one of the causes of Cossiga's death. He had been re-attached to a life support machine after he suffered a "sudden and drastic deterioration" during the night, according to doctors.
Cossiga will be buried in his native Sardinia.
Italian head of state from 1985 to 1992 and a staunch opponent of communism, Cossiga helped lead the country's fight against domestic terrorism in the 1980s.
A Christian Democrat politician from his teens, he was elected president aged 57, the youngest in Italy's history.
Before his death, Cossiga delivered a sealed envelope to the Italian Senate containing instructions for his funeral and letters to Italian president Giorgio Napolitano, to prime minister Silvio Berlusconi and Senate president Renato Schifani.
Cossiga was said to have been given the last rites last week, but his condition then improved before worsening irrevocably Tuesday.
Cossiga, who was also a former premier and interior minister, automatically became a life senator after serving as president.
In 1978, Cossiga resigned as interior minister in bitterness after failing to save the life of Christian Democratic leader Aldo Moro, who was kidnapped and murdered by the leftist Red Brigades during one of the most turbulent periods in Italy's post-World War II history.
Near the end of his seven-year term as president, Cossiga was threatened with impeachment over his admission that he had played a key role in an alleged, clandestine US-sponsored military organisation known as Gladio (sword).