Oscar Pistorius, released from jail under house arrest last month, could return to prison if the appeal by South African prosecutors is successful.
The double amputee was convicted of culpable homicide, the equivalent of manslaughter, after he shot his girlfriend Reeva Steenkamp through a locked toilet door in 2013. Pistorius was released from prison under "correctional supervision" on 19 October, having served a sixth of his five year sentence.
On Tuesday, five of South Africa's most senior judges heard prosecutor Gerrie Nel outline the state's appeal for the verdict to be changed from culpable homicide to murder, particularly the charge of dolus eventualis, also known as common-law murder.
In South African law, this charge applies if the accused knew they might kill someone but still proceeded with their course of action.
During his trial, Pistorius claimed that he believed there was an intruder in the house and thought his girlfriend was in the bedroom. However, the prosecution has argued that who was behind the toilet door was irrelevant, and Pistorius should have foreseen that by firing four shots through the door, the person would have been killed
Pistorius and his family did not attend the hearing at South Africa's Supreme Court of Appeal in Bloemfontein, but Reeva's mother June Steenkamp was present.
Reeva Steenkamp's relatives have said they think Pistorius is "getting off lightly" after killing the model and law student.
The appeal court has reserved its judgment, and has not given a date for this to be revealed. If the judges rule in the prosecution's favour, the Paralympian's sentence could be increased from five years to a minimum of 15 years.