Cardiac electrophysiology (EP) has rapidly evolved in recent decades from targeting simple arrhythmias such as accessory pathway or nodal re-entry tachycardia to the ablation of more complex substrates. This evolution has been possible due to a better understanding of the anatomical basis, and hence the mechanism, of more complex cardiac arrhythmias. Imaging of the heart has played an important role in defining cardiac structures and characterising the arrhythmic substrates. In this regard, MRI has provided the most comprehensive evaluation of cardiac anatomy, function, and tissue characterisation, and has made a major contribution to the increase in ablation procedures. This article provides a comprehensive overview of the role of MRI in the management of the most common complex arrhythmias: atrial fibrillation (AF) and ventricular tachycardia (VT).