Disturbances in the propagation of the electrical wavefront can cause cardiac arrhythmia’s that can, in extreme cases, lead to cardiac arrest. By recording the electrical signals of the heart, a better understanding can be gained of the mechanisms behind cardiac arrhythmias. A method that can be used to investigate the state of the heart is electroanatomic mapping (EAM), where the local electrical activity is related to a point within a 3D anatomical reconstruction of the heart. By investigating the electrical activity, areas of scarring can be identified. Currently, the electrical activity is recorded with a plaque multi-electrode array at the Erasmus MC. Local activation maps can be recorded during sinus rhythm (SR), and with the use of a reference electrode, total activation maps are generated. This can only be done during SR. During arrhythmia’s, this is no longer possible due to temporal variation in electrical activity. To investigate the activation maps during arrhythmia, an electrode array that can record the total activity of the ventricles was designed and developed in this thesis. By studying the literature and with the help of medical experts, a requirement list was established. Different concept ideas were compared using a Harris profile to select the best design for further development. From the Harris profile it was concluded that a 3D printed sock was the best design for the electrode array. An investigation of the effects of the pattern and thickness on the stiffness and fatigue life of the sock were performed with the help of tensile tests and fatigue tests. From the results of the tensile and fatigue tests, a decision for the design of the electrode array was made. A 3D printed sock with the optimized design and electrodes were used to make epicardial recordings on a porcine heart in an ex vivo heart perfusion setup. The electrical recordings were later analyzed and visualized on a 3D model of the heart. Even though the resolution of the electrode array was lower than that of the epicardial mappings performed at the Erasmus MC, the results obtained from the electrode array looked promising. This is the first study that has developed a 3D printed electrode array the can record the electrical activity of the ventricular surface from multiple sites simultaneously. However, before the electrode array can be used for elucidating the mysteries behind epicardial activation during arrhythmia’s, further development is needed.