"We have detained a man for attempted murder with an alternative charge of aggravated assault," said Kent Lind at Dalarna police to the Aftonbladet daily.
The woman is reported to have gone home to her former partner on Saturday evening to leave their 5-year-old daughter and to inform him that she had begun a new relationship.
According to information from several family members, the man became angry, poured petrol over her and set her alight.
The woman sustained severe burns in the attack and is currently in the care of Linköping University Hospital.
According to information obtained by the newspaper the woman is very badly hurt and will be keep in a drug-induced coma for an extended period of time.
The former couple's five-year-old daughter is thought to have witnessed the attack.
The man was detained by police after the attack and was on Sunday formally arrested on suspicion of attempted murder with an alternative charge of aggravated assault.
Dalarna police were unwilling on Sunday to divulge further details of the case confirming only that a man had been arrested and that those involved had previously been in a relationship.