Experience of beriberi occurring among British and Australian prisoners of war indicated that heart block was not infrequent.There is no general agreement about the effect of thiamin deficiency on the heart, and in particular on cardiac conduction. The only electrocardiographic abnormality noted by Aalsmeer and Wenckebach (1929) was a shortening of the P-R interval. Keefer (1930) in 29 cases of beriberi noted no characteristic cardiographic change, though cardiac conduction was sometimes slightly altered: 15 of the 29 cases had evidence of cardiac insufficiency; these showed enlargement of the right auricle, right ventricle, pulmonary conus, and pulmonary artery. Jolliffe '(1939) in experimental thiamin deficiency found cardiographic changes in 2 of 5 human volunteers: in one, sinus arrhythmia, sinus arrest, and inversion of T III appeared after 11 days of deficiency, and in a second inversion of T III appeared after 8 days of deficiency. The changes reported by Weiss and Wilkins (1937) and by Dustin et al. (1939) included tachycardia, prolongation of electric systole, low voltage complexes, and flattening or inversion of T waves. Dock (1940) recorded 5 cases of idiopathic cardiac hypertrophy with mural thrombi thought to result from thiamin deficiency, in 4 of whom there was disturbance of conduction-right bundle branch block in 3 and latent A-V block in 1 case. Casanova (1946) observed flat bifid P waves, prolongation of the P-R interval, and auricular fibrillation (once) in beriberi.Most accounts of the pathology of the heart in beriberi have been limited to a description of the macroscopic abnormalities. It is uncertain whether the enlargement of the right side of the heart is due to dilatation alone or to dilatation combined with hypertrophy.Weiss and Wilkins (1937) found that the weight of the heart was generally normal and that there was a moderate dilatation of the right ventricle. Wenckebach (1934) and Weiss and Wilkins (1937) observed a " hydropic" degeneration of the muscle fibres.Disturbances of A-V conduction are not mentioned in most clinical accounts qf beriberi and lesions affecting the specialized muscle of the conducting system have not been noted on histological examination. Thus Blankenhorn (1945) gave as the first of the criteria for the diagnosis of beriberi heart disease " an enlarged heart with normal sino-auricular rhythm."As there is no general recognition of the appearance of conduction defects in human thiamin deficiency it was thought advisable to record the clinical impression of its not infrequent occurrence. In the light of our clinical experience it was considered that analysis of the effects upon cardiac conduction of prolonged severe thiamin deficiency in animals would be of value and should determine whether the changes present had a functional or organic basis. EXPERIMENTAL METHODSPigs were used since they are known to be the animals most susceptible to thiamin deficiency. The animals were obtained when five weeks old. The dietetic method was largely that of Wintrobe (19...

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