Whenever there is a dropped beat or an intermittent pulse one may be sure that it is the result of an extrasystole. Such extrasystoles are produced in the ventricle at some point other than the regular path of conduction of impulses. The extrasystole may have its origin in either the auricle or the ventricle. If there is auricular extrasystole it can not usually be recognized except by graphic methods. (Fig. 45.) The ventricular extrasystole on the contrary is commonly seen and readily recognized. Most of those seen in the clinic have their origin in some part of the ventricular wall. Their two characteristics are that they occur too early and that they are followed by a pause longer than the normal diastolic pause. (Fig. 46.) [Illustration: Fig. 45.--Electrocardiogram showing auricular extrasystoles (P). (Courtesy of Dr. G. C. Robinson.)] [Illustration: Fig. 46.--Electrocardiogram showing ventricular extrasystole. Heart rate 56-60 beats per minute. Note that diastolic pause in which extrasystole occurs is practically equal to two normal diastolic pauses. (Courtesy of Dr. G. C. Robinson.)] When one listens over the chest to a heart when extrasystoles are occurring, one suddenly hears a weak beat which has taken place rather too early after the previous systole to be strong enough to effect the opening of the aortic valves. Consequently there is no pulse, the blood does not move, and that beat is lost to the circulation. Moreover, when the next regular stimulus comes from the s-a node it finds the ventricle in a refractory condition, having just ceased a contraction, and it is not until the next sinus impulse that the ventricle responds normally. (Fig. 46.) Patients who have occasional extrasystoles will say that all of a sudden the heart turns upside down in the chest. Sometimes there is slight sharp twinge of pain. Patients are at times quite alarmed about their condition. Provided there is no evidence of gross myocardial lesion, the extrasystole itself is of no great significance. While many cases showing pathologic causes for extrasystoles have more or less marked arteriosclerosis, there are other states in which no arteriosclerosis is found where the extrasystole is present. =Heart Block=