Surgeons of the Mayo Clinic, in a report[134] on Operative Risk in Cardiac Disease, hold that a valvular lesion is not a rational basis for judging a cardiopath so far as prognosis in a surgical operation is concerned, but this statement is not true for an obstetrical case. If we except angina pectoris and related diseases, the four disorders of the heart's mechanism that surgeons deem the worst risks in operation are auricular fibrillation, auricular flutter, impaired auriculoventricular conduction, and impaired intraventricular conduction. These conditions are usually accompanied by extensive lesions of the heart muscle. [134] _Jour. Amer. Med. Assoc._, lxix, 24. In auricular fibrillation there are rapid incoördinate contractions, twitchings in individual muscle bundles of the auricular wall. The auricle loses its power to pump the blood and dilates. The pulse is commonly arhythmic and rapid. A permanent fibrillation is worse than a paroxysmal state. The condition is found especially in advanced cases of exophthalmic goitre. In the Mayo Clinic the operative mortality in seventy cases of exophthalmic goitre with auricular fibrillation was only 2.8 per cent. In auricular flutter, or heart block, there are foci of irritation in the auricular wall which cause rapid coördinate contractions. The auricle may contract twice as often as the ventricle, and the pulse may be regular or markedly irregular. The stimulus for heart contraction normally reaches the ventricle from the auricle by passing along the bridge of primitive tissue which connects the auricle and ventricle. This bridge may be so affected that the stimulus is delayed, or prevented at times from crossing over, or completely blocked. One patient with complete heart block was operated upon at the Mayo Clinic three times in eleven years for appendicitis, cancer of the breast, and the excision of recurring skin nodules, and is still alive and reasonably well. In intraventricular block the risk of operation is worth taking, according to the opinion at the Mayo Clinic, where there is exophthalmic goitre or tonsillitis. In general, where there is question of surgical operation on a cardiopath, no such operation should be done unless there is definite ground to believe that the operation is essential to improve the heart condition or restore reasonable health. Extremely severe cardiac disease can be relieved or even completely cured by the surgical removal of infectious, mechanical, or toxic sources of heart degeneration, especially goitre. When the myocardial insufficiency is so marked that no medical treatment reëstablishes a reasonable compensation, no surgical operation is permissible. The medical treatment is the only test to learn whether the heart can be put into a condition wherein it will withstand the anesthesia and the operation. Life depends on ventricular action, not on auricular, and the ventricular reserve is the standard for judgment in these cases.