Though the surgery to separate Maria Jose Paredes Navarrete from her twin was initially called successful with few complications, the infant's condition grew increasingly unstable and critical until she died Sunday night, The Santiago Times reported.
The death was the result of "a flaw in the right side of the heart as a consequence of pulmonary hypertension that afflicted her since her birth," Calvo Mackenna Hospital said in a statement.
Conjoined twins Maria Paz and Maria Jose Paredes Navarrete were born in February, connected through their chest, abdomen, legs and pelvis with a shared intestine and liver.
Over 100 people participated in the separation surgery that lasted more than 18 hours.
"We are sure that we made every effort," hospital Director Osvaldo Artaza said of the attempt to save Maria Jose. "This is a moment of deep pain, of deep grieving."
Surviving twin Maria Paz remained in stable but critical condition, the hospital said.