Foxglove is the source of digoxin, a medicine used to treat congestive heart failure and heart rhythm problems. Foxglove is a biennial that sows itself freely in most parts of the United States if the seed pods are allowed to ripen. It can be grown in moist, well drained soil in USDA Hardiness Zones 4 through 8. Flowers are attractive to hummingbirds. Plant leaves, flowers and seeds of this plant are a source of the drug digitalis and are all poisonous to humans and some animals and can be fatal if eaten. Extracted from the leaves, this same compound (digoxin) is used as a medication for heart failure. Digoxigenin is a steroid found exclusively in the flowers and leaves of these plants (and Digitalis lanata) and it is used as a component of molecular probes to detect DNA or RNA. You can see foxglove in the National Herb Garden, where it is scattered throughout the Antique and Heritage Rose Garden and the Theme Gardens.