A device for occlusion of a body lumen such as the left atrial appendage of a mammalian heart is described. The device comprises an implantable occlusion apparatus (3) operably and detachably attached to an elongated catheter member (4) configured for transluminal delivery and deployment of the occlusion apparatus in the body lumen. The occlusion apparatus comprises a radially expansible element (5) that is adjustable between a contracted orientation suitable for transluminal delivery and a deployed orientation configured to occlude the body lumen, an energy delivery element (6, 14, 21) configured to deliver heat energy to surrounding tissue to heat the tissue, and a sensor (7) configured to detect a parameter of the wall of the body lumen. The sensor is an optical sensor that is configured to detect changes in blood flow in the wall of the body lumen, optionally distally of the radially expansible element.
