Although opium and its derivatives are not classed by pharmacologists with the so-called "cardiac" drugs, every practitioner can testify to their value in the treatment of cardiac and vascular conditions. All the great clinical authorities concede to morphin an undisputed place in the armamentarium of cardiac therapy. Osler,1for instance, speaks of it, for nocturnal dyspnea, restlessness and distressing feelings of anxiety, as "invaluable," and in angina pectoris, it is put second only to the volatile nitrites. Indeed, Krehl2places it first, when he says, "In severe cases morphin is indispensable; in selected cases amyl nitrite and nitroglycerin are of help."3The general impression seems to be that the opiates in heart disease do not act on the heart and vessels themselves, but indirectly through quieting the nervous system. The evidence for this theory is chiefly empirical, and considering the importance of opium in the Pharmacopeia, it