Abstract: A robotic catheter can include bi-stable concentric tubes and a torsional spring mechanism that can provide torque at the proximal extremity of one or more tubes. The robotic catheter can compensate for the energy that may be released by the tubes snapping from on stable-equilibrium position to another by using the energy stored in the torsional spring mechanism. The energy released by the tubes upon snapping from one stable-equilibrium position to the other can be compensated by the energy stored in the torsional spring at the base, thereby resulting in the first, energy-free, zero stiffness catheter system that (1) synchronizes with the motion of the heart and (2) naturally results in optimal, pseudo-constant contact force with the tissue.