Occluder, comprising a continuous tubular braided structure made of an integral base body of at least one wire and having a pitch, said pitch varies along an axial length of the base body with at least one pitch transition section; the occluder being heat set to have a shape including; a proximal retention element having an outer circumference and a distal inner diameter at a first transition section in a relaxed state of the occluder; a distal retention element having an outer circumference and a proximal inner diameter at a second transition section in the relaxed state of the occluder; an intermediate element extending between the first and second transition sections (9a, 9b) of the proximal retention element and the distal retention element, wherein - the occluder is extendible from the relaxed state to an axially extended state, which is longer in the longitudinal direction of the occluder, than the relaxed state, and wherein the load to extension ratio, measured in N/mm, provided by the occluder is less than about 0.75 when extended at least 2 mm, without distortion of the proximal or distal retention elements, and wherein - a position of at least one of said transition sections (9a, 9b) is closer to a central axis of the occluder, and a diameter of said intermediate element is reduced from a relaxed diameter thereof, when the occluder is in the axially extended state. - characterized in that the outer circumference of at least one of the proximal retention element and the distal retention element is substantially constant when the occluder is extended in length more than 50% of the relaxed state and up to about 150% of the relaxed state. a continuous tubular braided structure made of an integral base body of at least one wire and having a pitch, said pitch varies along an axial length of the base body with at least one pitch transition section; the occluder being heat set to have a shape including; a proximal retention element having an outer circumference and a distal inner diameter at a first transition section in a relaxed state of the occluder; a distal retention element having an outer circumference and a proximal inner diameter at a second transition section in the relaxed state of the occluder; an intermediate element extending between the first and second transition sections (9a, 9b) of the proximal retention element and the distal retention element, wherein - the occluder is extendible from the relaxed state to an axially extended state, which is longer in the longitudinal direction of the occluder, than the relaxed state, and wherein the load to extension ratio, measured in N/mm, provided by the occluder is less than about 0.75 when extended at least 2 mm, without distortion of the proximal or distal retention elements, and wherein - a position of at least one of said transition sections (9a, 9b) is closer to a central axis of the occluder, and a diameter of said intermediate element is reduced from a relaxed diameter thereof, when the occluder is in the axially extended state. - characterized in that the outer circumference of at least one of the proximal retention element and the distal retention element is substantially constant when the occluder is extended in length more than 50% of the relaxed state and up to about 150% of the relaxed state. - the occluder is extendible from the relaxed state to an axially extended state, which is longer in the longitudinal direction of the occluder, than the relaxed state, and wherein the load to extension ratio, measured in N/mm, provided by the occluder is less than about 0.75 when extended at least 2 mm, without distortion of the proximal or distal retention elements, and wherein - a position of at least one of said transition sections (9a, 9b) is closer to a central axis of the occluder, and a diameter of said intermediate element is reduced from a relaxed diameter thereof, when the occluder is in the axially extended state. - characterized in that the outer circumference of at least one of the proximal retention element and the distal retention element is substantially constant when the occluder is extended in length more than 50% of the relaxed state and up to about 150% of the relaxed state.