Gen Pinochet celebrated his 91st birthday a week ago
Gen Pinochet's life
The 91-year-old needs a second intervention, state media has reported medics treating him as saying.
The former leader, who was put under house arrest a few days ago, is in a military hospital in Santiago.
Gen Pinochet was in power from 1973-90, during which time more than 3,000 people were killed or "disappeared".
He is accused of dozens of human rights violations but has never faced trial because of poor health.
Angioplasty procedure
He was taken to hospital early on Sunday morning after suffering "an acute" heart attack and a build-up of fluid on his lungs, a statement from the hospital said.
Doctors had carried out "procedures that rescued him virtually from death," Gen Pinochet's son, Marco Antonio Pinochet told reporters gathered outside the hospital.
"He's in a pretty serious state...We're in the hands of God and the doctors."
The former leader received the last rites from a Catholic priest, a family spokesman said.
One of the medical staff, Dr Juan Ignacio Vergara, said Gen Pinochet was in a stable condition but his life was not out of danger.
Gen Pinochet underwent angioplasty, a procedure designed to widen a narrowed or totally obstructed blood vessel, to stabilise his condition, he said.
Now, according to reports on Chilean state television, he needs a second operation - possibly a heart by-pass.
'Political responsibility'
General Pinochet overthrew the elected government of the left-wing President Salvador Allende in 1973 in a bloody coup.
He was placed under house arrest earlier this week over the abduction of two people in 1973.
The charges relate to the Caravan of Death - a military operation to remove opponents to Gen Pinochet's rule.
He currently faces two other indictments - one for human rights abuses and another for tax evasion.
As a former president he enjoys legal immunity, but the courts can strip him of this privilege on a case-by-case basis.
On 25 November, his 91st birthday, Gen Pinochet issued a statement in which he took "political responsibility" for acts that took place under his rule, saying that he had believed they were in Chile's best interests.
He also alluded to his failing health.
"Today, close to the end of my days, I want to make clear that I hold no rancour toward anybody, that I love my country above all else," he said.
Gen Pinochet has been in ill health in recent years. He suffers from diabetes and arthritis, and has also had a number of suspected strokes.
Der 91-jährige ehemalige Diktator Chiles, Augusto Pinochet, hat einen Herzinfarkt erlitten und schwebt in Lebensgefahr. Er war heute morgen in das Militärkrankenhaus in Chile eingeliefert worden und hat dort inzwischen die letzte Ölung bekommen. Das wurde vom Sprecher der Familie Pinochets, General Guillermo Garín, in Santiago de Chile mitgeteilt. Laut dem Krankenhaus wurde ihm ein Bypass gelegt, er schwebe aber weiterhin in Lebensgefahr.

Pinochet stand von 1973, nachdem er in einem blutigen Umsturz die Macht an sich gerissen hatte, bis 1990 an der Spitze des südamerikanischen Landes. Während dieser Zeit sind mehr als 3.000 Leute umgebracht worden oder einfach „verschwunden“. Ihm werden haufenweise Menschenrechtsverletzungen vorgeworfen. Aufgrund seines schon länger schlechten Gesundheitszustandes und wegen seiner Immunität als ehemaliger Präsident des Landes wurde er bislang aber nie verurteilt. Diese Woche wurde er wegen der Entführung zweier Leute im Jahre 1973 unter Hausarrest gestellt.

Zu seinem 91. Geburtstag, am 25. November 2006, übernahm er die „politische Verantwortung“ für die Taten, die unter seiner Herrschaft geschehen waren, betonte aber gleichzeitig, dass er geglaubt habe, diese Taten seien nur zum Besten von Chile.