Toxic Agent
Many of the common names of this plant pertain to its toxic nature (Witches' glove, Dead Man's Bells, Bloody Fingers). Foxglove belongs to the Figwort family (Scrophulariaceae) and the whole plant is toxic. It contains various cardiac glycosides. Symptoms include dizziness, vomiting, irregular heart beat, and delerium or halucinations.
Digitonin is a Digitalis drug derived from D. purpurea. It is used in modern medicine to increase the force of the systolic contractions and prolong duration of the diastolic phase in congestive heart failure. Digitalis drugs lower venous pressure in hypersensetive heart ailments, elevate blood pressure in a weak heart act as a diuretic, and reduce edema. However, the theraputic dose is dangerously close to the lethal dose. Historically, Foxglove was employed by herbalists for a variety of purposes, fom an ointment used for cleansing wounds and reducing swelling to boiling it and using it as an expectorant.
There are a number of plants containing glycosides (including Lily of the Valley), which are toxic to a wide range of animals including humans.
More information describing Foxglove is available under the listing for Digitalis purpurea, Foxglove, in the Canadian Poisonous Plants Information System, courtesy of Derek B. Munro.