Leadless pacemaker, including a hermetic housing, a pacing electrode on a distal portion of the housing, an electronics package in the housing and configured to generate/deliver pacing pulses to the electrode, and a fixation mechanism on the housing distal portion. The fixation mechanism includes at least one deformable hook-shaped thin fixation wire having an attachment portion fixedly attached at the distal portion of the housing and a free end portion which is angled or bent with respect to the attachment portion such that it extends essentially in conformity, but with a small spacing, to a neighbored surface portion of the housing such that the free end portion engages with heart tissue onto which the distal portion is pressed upon rotation of the pacemaker in the direction in which the free end portion extends from the attachment portion, and disengages upon rotation of the pacemaker in the opposite direction.
