An indicator device for visually indicating a pressure of blood inside a blood vessel includes: a body, the body comprising a duct extending in the body and having a sealed proximal end; a distal end portion adapted to be positioned inside the blood vessel and including a liquid inlet opening in fluid communication with the duct; and a window including an at least semi-transparent section configured to enable visual observation of blood entering into the duct via the inlet opening when the inlet opening is located inside the blood vessel.