Toxic Principle and Mechanism of Action Nerium oleander contains numerous cardenolides and their genins that are concentrated in the leaves, flowers, and seeds.1,2 Also present in the plant are terpenoids that possibily account for the gastrointestinal irritation seen with oleander poisoning. The cardiotoxic effect of the oleander cardenolides is similar to that caused by digitoxin and digoxin found in the Digitalis species. The primary action of the cardenolides is on the cell membrane, where interference with normal transport of sodium and potassium ions across the cell membrane occurs allowing an influx of calcium.3 At low doses, myocardial function may improve, but at high doses cardiac conduction is impaired with resulting arrhythmias, heart block, and death.