Detectives have arrested a 34-year-old woman on suspicion of murder following an incident at an address in Parr, St Helens on Tuesday, December 27.
Officers were called to an address on Cross Farm Road, Parr, at about 7.20pm after paramedics had attended at the house and found a man with a stab wound to his chest.
Paramedics tended to the victim at the scene, but he died in the ambulance while en route to hospital.
Crimes Scene Investigators are carrying out forensic examinations at the scene and House-to-house inquiries are under way.
Anyone who has any information which could help the police with their inquiries is asked to contact 101, or Crimestoppers on 0800 555 111.