Lily-of-the-valley is poisonous to humans and animals as it contains toxic cardiac glycosides
. All parts of the plant contain these toxic compounds, with the seeds and flowers having the highest concentration
. Even drying the plant does not render its toxic compounds harmless
. Due to its strong effect on the heart, lily-of-the-valley was used in folk medicine as early as the 15th century, and modern orthodox medicine uses tolerable minute quantities as active ingredients in medicines
. Lily-of-the-valley is likely unsafe when taken by mouth while pregnant or breastfeeding, and it contains chemicals that can make heart disease worse
. It is also unsafe to use lily-of-the-valley if you have low potassium levels
