Former president Fernando de la Rúa was hospitalised on Tuesday after suffering an acute episode of bronchitis and a heart attack during the New Year holiday.
Argentina's head of state from 1999 to 2001 was in a "serious condition" at the Austral University Hospital in Pilar, near Buenos Aires City, his relatives told local media. He was said to be in intensive care, with his wife and two sons keeping a bedside vigil.
According to a report published by the Télam state news agency, a medical source told reporters "he's in a delicate state."
De la Rúa, 81, was with his family at the Villa Rosa estate near Pilar when he suddenly fell ill on January 1.
He was previously hospitalised at the Diagnostic Institute in the City's Recoleta neighbourhood after a heart attack in October. In May, following a similar episode, doctors gave him two stents.
De la Rúa's heart problems date back to 2001 during his brief time as president, when he was hospitalised for a heart problem while serving as head of state. He had an operation to open a clogged heart artery in 2014, while he also had cardiac problems requiring surgery in both 2017 and 2018.
His last public appearance was on November 30 during a gala at the Teatro Colón for visiting heads of G20 member states.
De la Rúa's political career began in the early 1970s when he unsuccessfully ran for vice-president alongside Radical Party (UCR) presidential candidate Ricardo Balbín.
Following several tenures as a congressman during the 1980s and 1990s, he led a coalition of parties to win the presidency in 1999 against the Peronists.
His short time in office was marred by instability. In particular, De la Rúa's legacy is tied to the Corralito, an economic measure his government implemented in late 2001 to stop a run on the banks. Hugely unpopular, it almost completely froze bank accounts and forbade withdrawals from US dollar-denominated accounts.
De la Rúa famously fled the Casa Rosada government palace in a helicopter during deadly riots in December 2001, effectively marking an end to his presidency.