Cardiac sedatives are substances which lessen the force and frequency of the heart's action.

They are chiefly used, either for the purpose of lessening violent action or palpitation of the heart, or of rendering the pulse slower in febrile conditions, especially those consequent on local inflammation. It has already been mentioned that belladonna diminishes the sensibility of the heart to changes of pressure, and that sometimes it is useful in palpitation consequent on cardiac strain. Simple pressure over the cardiac region appears to have the power of lessening palpitation, so that when this occurs in consequence of any sudden emotion, there is a natural tendency to press the hand over the region of the heart. It is impossible to say whether the relief which such pressure certainly affords is simply mechanical, or is due to reflex action on the heart through the cutaneous nerves. Plasters applied to the cardiac region have a beneficial action upon palpitation similar to that of the hand, and one of the most commonly used and beneficial is belladonna plaster. In irritable-heart of soldiers Dr. Da Costa found digitalis better than any other remedy.1

In palpitation depending on indigestion, hydrocyanic acid is useful. In palpitation due to aortic disease, senega has been recommended. It is probable that its efficacy depends upon the diminished action of the cardiac ganglia and muscle which its active principle, saponine, produces.

An active circulation of blood is usually advantageous both for functional activity and for the repair of damage to an organ, but sometimes it may become excessive, and relief may be afforded by diminishing it (vide p. 342).

1 Amer. Journ. Med. Sci., Jan. 1871.

The chief cardiac sedatives employed for this purpose are :Aconite.

Veratrum viride. Antimonial preparations.

It is questionable whether in extensive inflammation of internal organs cardiac sedatives are of much service or not. They seem, however, to give relief in the feverish condition which accompanies more limited inflammation, such as tonsillitis, otitis, etc. In such cases the tincture of aconite is best employed in very small doses (one drop) frequently repeated. The introduction of this method of using the drug in divided doses is due in great measure to Ringer, and it has the very great advantage that the desired effect can be produced with greater certainty and with less risk of an overdose being given.