Using robotic systems to assist with sophisticated medical interventions such as aortic valve replacement under beating heart conditions necessitates the development of dexterous manipulators to ensure a safe and reliable operation. These mechanisms should not only be capable of tracking the desired trajectories with a high level of accuracy but also need to cope with strict medical constraints such as environment compatibility, patient safety and compactness. In this paper, we propose to design and experimentally qualify a robotic platform that takes into account the aforementioned requirements. Benefiting from the features of a parallel architecture, this four degrees of freedom (DOF) magnetic resonance imaging (MRI)-compatible patient-mounted and cable-driven manipulator (ROBOCATHETER) seeks to steer cardiac catheters under beating heart condition, while suitably addressing the deficiencies that currently used manipulators vastly suffer from. In addition to the detailed description of the robot design and its dedicated power transmission system, we also present the derivation of the robot's forward and inverse kinematic equations. The control algorithm implemented for the system actuation is a varying-gain proportional-integral-derivative (PID) controller, whose tracking performance will be examined.