In 1895, Willem Einthoven described the waves recorded from his invention, the string galvanometer. His PQRST diagram is remarkably similar to the P, QRS, and T waves currently used daily by cardiologists everywhere for interpretation of a standard electrocardiogram (ECG). Therefore, it may appear that little has changed with respect to the image, principles, and nomenclature of a standard ECG tracing over the past century. However, tremendous changes have been made in the method of ECG recordings. For instance, there is no longer a need to immerse limbs in saline, precordial and unipolar electrodes have been developed, and digital/computerized recording systems have been implemented. Similar advancements have also been made in our understanding of electrical signals recorded from within the heart (intracardiac recordings) since the recording of the first His bundle. During the past half-century, we have witnessed the development of cardiopulmonary resuscitation, transthoracic cardioversion and defibrillation, and the advent of implantable devices (pacemakers, defibrillators, loop recorders, and biventricular devices). Innovations in catheter ablation have resulted in a very high success rate for most reentrant and focal supraventricular tachycardias and certain ventricular tachycardias. Even atrial fibrillation can be successfully managed in many circumstances via pulmonary vein isolation procedures and left atrial ablations. These procedures can be performed percutaneously with an ablation catheter.