These are drugs which have no perceptible immediate action on the heart, but when given for a little while render its beats much more powerful, although usually much slower. The most important of them are :Digitalis.

Digitalin.

Digitalein.

Digitoxin. Erythrophloeum (Casca)

Erythrophloein. Strophanthus hispidus.

Strophanthin.

Convallaria majalis.

Convallamarin. Adonis vernalis.

Adonidin. Squills.

Scillain. Helleborein. Antiarin. Caffeine. Nux vomica.

Strychnine.

All these drugs, as already mentioned, stimulate the cardiac muscle and render its contractions slower and stronger. Although in large doses they tend themselves to produce irregular and peristaltic contraction of the heart, yet in moderate doses they tend to remove irregularity already present. The cases in which they are most useful are those in which the left ventricle is unable to drive the blood with sufficient force into the aorta. It is evident that this inability may depend on simple weakness of the ventricle without any valvular lesion, or upon irregular action of the various cavities, or upon valvular lesions, or on a combination of two or more of these conditions.

Weakness of the heart may occur in cases of general malnutrition, as anaemia and chlorosis, or in consequence of acute disease such as fevers. It is not necessarily accompanied by dilatation, but if it continues for some time the cavities are apt to dilate. A considerable amount of dilatation may sometimes occur without leading to valvular incompetence, but if it proceeds beyond a certain point the cusps of the tricuspid and mitral valves become insufficient to close the dilated orifices, and mitral or tricuspid regurgitation is the result. For it must be remembered that in the healthy heart the tricuspid and mitral orifices are much diminished in size by the contraction of the muscular tissue of the heart at the moment of systole.

In cases where the mitral valve is thus affected, a systolic murmur may be heard at the apex during life, but, should death occur, the valves may be found perfectly competent to close the mitral orifice in the heart, which is then in a state of more or less complete rigor. In all such cases of weakness of the heart, either with or without dilatation and functional incompetence of the valves, digitalis is of the greatest possible service. I have also found erythrophloeum give most satisfactory results in simple dilatation without incompetence.

The form of valvular disease in which cardiac tonics are especially useful is mitral regurgitation. In all forms of valvular disease there is a tendency to the occurrence of compensatory hypertrophy, which will enable the heart to do its work in spite of the hindrance caused by the disease. Wherever this is sufficient, so that the circulation is well carried on, notwithstanding the valvular defect, cardiac tonics are useless and likely to be injurious. Nor should they be given when the compensatory hypertrophy is just beginning to take place. But when compensation is insufficient, cardiac tonics are of the very highest value. In mitral regurgitation the blood, instead of being driven entirely onwards by the left ventricle into the aorta, is partially driven backwards into the left auricle at the very moment that the right ventricle is driving the blood into the pulmonary artery and lungs. Hence there is a tendency to pulmonary congestion, which may lead to haemoptysis. The right ventricle having to work against greatly increased pressure tends to dilate, the blood accumulates in the venous system generally, and venous congestion of the stomach leads to loss of appetite, of the kidneys to albuminuria, and of the limbs to anasarca. While the venous system is gorged, the arterial is correspondingly empty, and it is not only the stomach, kidneys, and limbs which suffer by the stagnation of the circulation, for a similar condition exists in the heart itself. In consequence of this its action may become not only weak but irregular, and matters go on from bad to worse.

In such a condition cardiac tonics are of the greatest possible service. By increasing the strength of the cardiac muscle they not only enable the left ventricle to drive a larger proportion of blood into the aorta, but they actually tend to lessen the opening of the mitral orifice in the same way as in functional incompetence. By rendering the pulse less frequent they allow the ventricle to become more completely filled during each diastole. The pressure on the lungs, right side of the heart, and venous system is diminished, the arterial system becomes correspondingly filled, the congestion of the various organs is diminished and their function correspondingly improved.

The consequence of this is, that in the stomach we have increased appetite, in the kidneys diminished albumen, and in the limbs removal of anasarca. The heart also benefits by the improved circulation in it, its pulsations are more regular and powerful, and it will often continue to act well and carry on the circulation satisfactorily even after the tonics which first enabled it to do so have been discontinued.

In mitral stenosis cardiac tonics probably are beneficial both by lengthening the diastole, and thus allowing more time for the blood to run out of the auricle into the ventricle, and by strengthening the auricle itself. Besides this, mitral stenosis is usually accompanied by mitral regurgitation, which will be benefited by cardiac tonics in the way just described.

In aortic stenosis digitalis is of little or no use when there is sufficient compensatory hypertrophy, but may be useful if the heart is becoming feeble.

There has been considerable difference of opinion regarding the use of digitalis in aortic regurgitation, some holding it to be useful and unattended with any risk, while others regard its administration as attended with considerable danger. In considering this question we must bear in mind that the risks which a patient runs from aortic regurgitation are not the same in all stages of the disease. While the aortic regurgitation is uncomplicated, and the ventricle strong enough to carry on the circulation, the risk to the patient is that of sudden death by syncope.

It is easy to understand how this should be the case. When the aortic valves are healthy the arterial system may be regarded as a large-branched tube open only at one end - the capillaries - and through these the blood flows so slowly that there is no risk of syncope from the blood-pressure falling too low (Fig. 118, a).

In a case of aortic regurgitation, on the contrary, the arterial system is open at both ends, and during the cardiac diastole the blood is not only running through the capillaries, but is running backwards into the left ventricle, so that the conditions are favourable for the blood-pressure falling so low as to induce syncope (Fig. 118, b). It is evident that anything which prolongs the diastole, and thus allows more time for the arterial system to empty itself through the capillaries at one end and into the ventricle at the other, will increase the risk of syncope, and for this reason digitalis cannot be regarded as free from danger in aortic regurgitation. The danger may, however, be very considerably diminished by keeping the patient in a recumbent posture with the head low. The column of blood above the aortic valves being lower, there will be somewhat less tendency to regurgitation; and even should the arterial pressure fall much, the brain may still receive sufficient blood supply to prevent syncope.

Fig. 118.   Diagram to illustrate the tendency to syncope in aortic regurgitation. In a the aortic valves are healthy and prevent regurgitation. The carotid and its branches are shown as full.

Fig. 118. - Diagram to illustrate the tendency to syncope in aortic regurgitation. In a the aortic valves are healthy and prevent regurgitation. The carotid and its branches are shown as full. In b there is aortic regurgitation, the blood flows out of the arterial system through the capillaries and into the heart. The carotid and its branches are shown as empty. In c the condition is the same as in b, but the patient is supposed to be in the recumbent posture, and the carotid and its branches remain full.

In cases of aortic disease, where compensatory hypertrophy is insufficient, or where the hypertrophied heart is becoming enfeebled and dilated so that the mitral valves no longer close the orifice, the most urgent risk to the patient is no longer that of sudden syncope, but of pulmonary embarrassment, dropsy, and all the other consequences of mitral regurgitation. In such cases, as well as in those where organic disease of both mitral and aortic valves exist simultaneously, we must treat the urgent symptoms and give digitalis or other cardiac tonics.

In dilatation of the right heart due to bronchitis or emphysema, digitalis is frequently useful, though its benefit is less marked than in mitral disease.