A 10-month-old Chilean girl has died after a 20-hour surgery last week to separate her from her conjoined twin, who is expected to live.
Maria Jose died "despite all medical efforts, as a result of deficiencies in several of her organs, mainly associated with heart problems", Osvaldo Artaza, the director of the Hospital Luis Calvo Mackenna, told reporters on Monday.
The surviving twin, Maria Paz, woke up earlier yesterday, according to Juan Carlos Acuna, head of the intensive care unit, who said it was an "excellent sign" that she would recover from the surgery.
"Hopefully, we will have a favourable outcome. Every day we make progress," Acuna said.
Maria Jose, who was smaller than her twin, had been in critical condition following an arrhythmia episode on Thursday that required resuscitation efforts.
The operation to separate the twins - who were conjoined at the chest and pelvis - involved separating the thorax, liver, intestines and pelvis and then reconstruction of their organs and surrounding tissue.
Some 100 professionals worked in rotating shifts of 24 to complete the marathon surgery, which began on Tuesday. An earlier procedure two months earlier separated a leg shared by the twins.
The girls are the daughters of a truck driver and a housewife from the southern town of Loncoche.
Health Minister Jaime Manalich, who visited the twins last week, said the Chilean government is paying for the procedure, which hospital officials said would cost more than US$200,000 (A$264,000).
In 1993 two conjoined twin boys were separated successfully in the same hospital in an operation that lasted more than 10 hours.