Emergency physicians routinely evaluate and manage poisoned patients. In 2003, more than 2 million human exposure cases were reported to poison centers throughout the United States [1]. Of those cases, 22% were treated in a health care facility with most of those cases evaluated in the emergency department. Cardiovascular drugs were listed as the fifteenth most frequently encountered human exposure (66,401) and the fifth leading cause of poisoning deaths.Drug-induced changes and abnormalities on the 12-lead electrocardiogram (ECG) are common. There are numerous drugs that can cause ECG changes and lead to cardiac dysrhythmias. The diagnoses and subsequent management of patients manifesting ECG changes following poisonings can challenge even the most experienced physician. Drugs that are advocated in Advanced Coronary Life Support protocols for cardiac dysrhythmias may not apply or may even worsen the condition of overdose patients [2].Despite that drugs have widely varying indications for therapeutic use, many unrelated drugs share a common cardiac pharmacologic effect if taken in overdose. The purpose of this article is to group together agents that cause similar electrocardiographic effects, review their pharmacologic actions, and discuss the electrocardiographic findings reported in the medical literature. The five main categories reviewed include potassium (Kþ) efflux blockers, sodium (Naþ) channel blockers, sodium-potassium adenosine-triphosphatase (Naþ/Kþ ATPase) blockers, calcium channel blockers (CCB), and beta-adrenergic blockers (BB). It is important to keep in mind, however, that many medications have actions that involve more than one of these