Digitalis is a drug widely used in the treatment of heart disease. It is obtained from the dried leaf of the purple foxglove plant (Digitalis purpurea). The term "digitalis" is used to refer to a whole class of glycosides found in various plants, all having characteristic pharmacological effects on the heart.

Digitalis is most commonly used to treat congestive heart failure; it is particularly effective when the congestive heart failure is caused by hypertension or arteriosclerotic heart disease. Digitalis is also used to slow the abnormally rapid cardiac rate found in cases of atrial fibrillation.

The most important action of digitalis is to increase the contractile power of the heart by acting directly on the heart muscle, or myocardium. This increase in the contractility of the heart muscle has no advantage in a normal person or animal, but in patients with heart disease in which the contractile power of the heart cannot keep up with the body's demand for heart action, digitalis has a most useful and strengthening effect on cardiac action. Other effects of digitalis include a slowing of the cardiac rate, an increase in cardiac output, and a decrease in the size of the heart. Digitalis will also increase urine secretion in patients who have edema caused by heart disease.

Only very small doses of digitalis are necessary to increase the contractile power of the heart. When the therapeutic doses are exceeded, digitalis can produce distinctly undesirable effects and even death.

Because digitalis also acts on enzymes that regulate ion transport across cellular membranes, it is of considerable interest to molecular biologists.

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