A heart rate measuring device is attached around a user's hand, the device having an inner surface, which is in contact with the skin on the hand to which it is attached, and an outer surface, which is other than the inner surface. The inner surface of the measuring device is provided with an electrically conductive inner structure, which functions as an electrode for a contact with the skin of the hand to which the device is attached. An electrically conductive outer structure functions as an electrode for a contact with the user's other hand and it is electrically isolated from the electrically conductive inner structure. The electrically conductive outer structure on the measuring device extends at least to opposite sides of the hand to which the device is attached, and at least part of the electrically conductive outer surface is on the outer surface of the measuring device, on opposite sides of the hand to which the device is attached. The electrically conductive outer structure and inner structure are connected to a measuring unit for heart rate measurement.