Abstract: The invention relates to an implantable medical device (1) for injecting and/or collecting fluid substance into and/or from an organism and comprising a chamber (2) delimited by a wall (3) which has at least one pierceable portion (4) in the area of which said wall (3) can be pierced through in the direction of its thickness (e) by a needle (5), said device comprising means (10) for transverse compression of the pierceable portion (4), and also retention means (20) designed to oppose the buckling, towards the outside of the device, experienced by the pierceable portion (4) under the effect of the compression (F1).