What is "cardiac glycoside"

n. obtained from a number of plants and used to stimulate the heart in cases of heart failure [syn: cardiac glucoside]

Cardiac glycosides are organic compounds containing a glycoside (sugar) that act on the contractile force of the cardiac muscle. Because of their potency in disrupting the function of the heart, most are extremely toxic. These glycosides are found as secondary metabolites in several plants, and in some insects, such as the milkweed butterflies, that consume the plants. In many terrestrial plants some pesticides are glycosides (as the cardiac digitoxin) and other cyanogenic glycosides which liberate cyanide, blocking cytochrome c oxidase and NIS,(poisonous for a large part of parasites and herbivores) causing a metabolic "cardiac hypothyroidism" with bradicardia and arrhythmia, and increasing calcium-induced calcium release. Chemically, the aglycone [non-sugar] part of cardiac glycoside is a steroidal moiety.