Of all the medicinal herbs for the heart, especially for heart problems associated with arteriosclerosis or hypertension, Foxglove is  without doubt the most beneficial.  However, this is also a very dangerous herb that can be fatal if taken inappropriately, with a thin margin between therapeutic and fatal dosage.  Thus, in the case of this herb, we are better off taking commercial preparations prescribed by our doctors and limiting the home use of this plant to the ornamental garden. 

There are many medicinal derivatives of foxglove, but the best known and most often prescribed for heart conditions is Digoxin, also called Lanoxin.  Overdose interferes with the electrical rhythm of the heart, causing irregular heartbeat, and also causes a variety of other symptoms including diarrhea, headache, and vomiting.  Because of variations of the amount of drug in the plant at any given time, correct dosages are near impossible to calculate, even by experienced herbalists. 

Foxglove is a classic example of why you should be educated about herbs before making any herbal preparations of your own.  The young plant can be easily mistaken for Comfrey or Plantain, and the consequences for making even one cup of herbal tea could be deadly if you have misidentified these herbs and gathered Foxglove instead. 

Every part of the Foxglove plant is poisonous, so if you have inquisitive little kids or pets who are inclined to chew, this is not an appropriate plant for the garden, although there are very few reports of animals ingesting it, suggesting that they somehow "know" not to bother it.