This special case-based issue of Cardiac Electrophysiology Clinics features a selection of cases on the following topics: Use of the Surface ECG to Define the Nature of Challenging Arrhythmias; Diagnostic and Prognostic Implications of Surface Recordings from Patients with A-V Block; Supraventricular Tachycardia; Ventricular Tachycardia; Atrial Fibrillation and Flutter; Troubleshooting Device Function; Adult Congenital Cardiac Disease; and Arrhythmias in Patients with Genetic Arrhythmia Syndromes.