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A short A-V conduction time, whether present with normal or with abnormal QRS complex, is associated with an increased incidence of paroxysmal rapid heart action. There are a considerable number of patients who have a short P-R interval, normal QRS complex and bouts of tachycardia. They are usually females, in middle life, devoid of organic heart disease and exhibit a snapping apical first heart sound. They do not demonstrate any of the features of anomalous A-V conduction. Evidence is presented suggesting the operation of endocrine and autonomic nervous system factors in the genesis both of the short P-R interval and the tachycardia.

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