Argentina's former President, Nestor Kirchner, has died after suffering a sudden heart attack, doctors say.
Mr Kirchner, 60, who had been operated on in September for heart problems, died in the southern Argentine city of El Calafate, local media reported.
His wife, Cristina Fernandez de Kirchner, is the current president of the country.
Mr Kirchner served as president from 2003 to 2007, and was being tipped to stand for election again in 2011.
The couple had faced some criticism within Argentina for appearing to get around presidential term limits by stepping aside for each other.
A lawyer by training, Mr Kirchner served as mayor of Rio Gallegos, his hometown in Argentina's Patagonian south, before becoming governor of the wider region - the oil and gas-rich province of Santa Cruz.
He was elected president after Argentina had seen a series of presidents come and go following a major financial crisis in 2001.
Mr Kirchner died with his wife by his side after being admitted to hospital in El Calafate in the early hours of Wednesday morning, reports said.
He "passed away due to a sudden death episode," Dr Luis Buonomo said.
There has been no statement from the Argentine presidency, but an official medical bulletin is expected later.
Mr Kirchner had been been dogged by ill health since leaving office in 2007 and had undergone two major operations in 2010 alone.
In February Mr Kirchner had surgery to remove a blockage in his carotid artery, which carries blood to the brain.
He had emergency angioplasty in September, when he complained of numbness in his legs and routine tests revealed a blocked coronary artery.
Since leaving office Mr Kirchner continued to remain politically active despite his health problems.
He had remained a member of the Argentine congress and secretary general of the South American regional grouping, Unasur.
With that role he maintained political influence beyond the borders of Argentina, playing a role in disputes and issues across South America, including in recent civil unrest in Ecuador.
I literally just heard about this--WTF. RIP to one of Argentina's fairly decent presidents in the last 50 years (granted, he and his wife have a lot of problems, but it was during his administration that the laws protecting the Dirty War criminals were overturned).