There are three types of basic ECG leads. These were developed by the cardiologists Einthoven, Goldberger, and Wilson. The first type are called the Einthoven limb leads, and these three leads are denoted by the Roman numerals I, II, and III. The second type are called the Goldberger augmented voltage limb leads, and these three leads are denoted by the abbreviation aV. The position of the aV lead on the patient is denoted by the addition of the letter L, R, or F: “aVL, as in left”; “aVR, as in right”; and “aVF, as in foot”. The third type are called the Wilson chest or precordial leads, and these six leads are denoted as V1 to V6. There are thus 12 basic ECG leads, which explains why we often speak of the 12-lead ECG. The limb leads provide a frontal view of the electrical activity of the heart, while the precordial leads provide a horizontal view. For certain clinical problems, additional precordial leads are used. More on that later.