The electrocardiogram (ECG) is a simple, rapid, accessible, and inexpensive diagnostic tool that continues to play a pivotal role in daily clinical activities. Through the practice of ECG interpretation, fundamental information is gathered to guide the approach of multiple cardiovascular disorders such as arrhythmias, acute coronary syndromes, conduction system abnormalities, preexcitation and long QT syndromes, pericardial syndromes, electrolyte disturbances, left ventricular hypertrophy, and side effects of drugs. This tool is indispensable for pharmacy personnel and other allied professionals. It is essential to understand its utility and learn to correctly interpret ECGs to provide adequate patient care. This chapter explains aspects of the heart’s conduction system physiology, nomenclature of electrocardiographic waves, and normality criteria. Furthermore, basic explanations of ECG pattern interpretation will be addressed. This will be done by specifically correlating rhythms with key cardiovascular disorders that are points of importance for pharmacists and other healthcare professionals.