An occluder device for occluding a cardiovascular defect or a gap between a medical device and adjacent body tissue, the occluder device comprising: a compliant balloon defining a balloon chamber; a tip element disposed at a distal side of the compliant balloon, a base element disposed at a proximal side of the compliant balloon, and connecting means comprising at least one connecting strut (9, 11, 12) attached to the tip element and to the base element; elongated actuating means, releasably connectable to the tip element, and longitudinally slidable with respect to the base element; locking means (2, 13) for maintaining a predetermined distance between the tip element and the base element; and proximal connector means for releasably connecting the occluder device to correspondingly configured distal connector means of a catheter device, characterised in that: the balloon chamber is fluid-tight; the compliant balloon is provided with a balloon channel forming a longitudinal passage from the proximal side to the distal side of the compliant balloon; the tip element and the base element each have a guide opening (105a, 105b) substantially coaxial to the balloon channel for slidingly receiving therein a guidewire for the device; the elongated actuating means are disposed longitudinally slidable in the balloon channel; and the compliant balloon comprises a fluid port for filling and unfilling a fluid into and from the balloon chamber. a compliant balloon defining a balloon chamber; a tip element disposed at a distal side of the compliant balloon, a base element disposed at a proximal side of the compliant balloon, and connecting means comprising at least one connecting strut (9, 11, 12) attached to the tip element and to the base element; elongated actuating means, releasably connectable to the tip element, and longitudinally slidable with respect to the base element; locking means (2, 13) for maintaining a predetermined distance between the tip element and the base element; and proximal connector means for releasably connecting the occluder device to correspondingly configured distal connector means of a catheter device, characterised in that: the balloon chamber is fluid-tight; the compliant balloon is provided with a balloon channel forming a longitudinal passage from the proximal side to the distal side of the compliant balloon; the tip element and the base element each have a guide opening (105a, 105b) substantially coaxial to the balloon channel for slidingly receiving therein a guidewire for the device; the elongated actuating means are disposed longitudinally slidable in the balloon channel; and the compliant balloon comprises a fluid port for filling and unfilling a fluid into and from the balloon chamber. the balloon chamber is fluid-tight; the compliant balloon is provided with a balloon channel forming a longitudinal passage from the proximal side to the distal side of the compliant balloon; the tip element and the base element each have a guide opening (105a, 105b) substantially coaxial to the balloon channel for slidingly receiving therein a guidewire for the device; the elongated actuating means are disposed longitudinally slidable in the balloon channel; and the compliant balloon comprises a fluid port for filling and unfilling a fluid into and from the balloon chamber.