Disturbances of conduction in the heart may be purely functional, when for example demands are made on the conduction path very early in diastole as seen in blocked and aberrantly conducted auricular extrasystoles (Scherf and Boyd, 1940), or when too many stimuli are presented for conduction within a short time as with the incomplete A-V block that always exists in auricular fibrillation. Conduction disturbances may also be due to vagal inhibition. They may occur transiently after pneumonia and influenza, and are well known in diphtheria; recently Neubauer (1942) found many examples of partial and complete block in 100 cases of diphtheria. Over-digitalization may through poisoning of the A-V node lead to prolongation of conduction time, partial, or complete block. A permanent block can be established through coronary sclerosis, coronary thrombosis, rheumatic heart disease, syphilitic gumma, and more rarely through diphtheria, tuberculosis, and carcinoma affecting the A-V node or bundle directly. Congenital complete heart block is also known, and a few cases were found by Yater (1929), Aitken (1932), Campbell and Suzman (1934), and Currie (1940. The exceptional event of heart block as a result of direct trauma to the chest wall is described by Coffen (1930), Walker (1933), and White (1937.The following is the report of a case in which complete heart block was associated with an intracardiac aneurysm and aortic stenosis.A farm labourer, 49 years of age, was admitted to the General Hospital, Northampton, on September 16, 1942. He had been off work since the beginning of July 1942, because of tiredness, dizziness, loss of weight, pains " all over the body," pain and frequency of micturition, and on one or two occasions attacks of haematuria. Mainly because of the urinary symptoms he was sent to hospital. Twenty years ago he had diphtheria, but had always enjoyed fairly good health otherwise, except for a regular winter cough. His father and one sister had died of tuberculosis. He was married and had three children aged 1, 7, and 10 years, who were all well; there had been one miscarriage and one stillbirth.On admission he complained of the above-mentioned symptoms, but his appetite was good and there was no cough, breathlessness, headache, vomiting, abdominal pain, or swelling of the ankles. He was pale and rather thin, but well built. Temp. 99, resp. rate 20, pulse rate 36. There was marked clubbing of the fingers and toes. The cardiac impulse was felt in the fifth intercostal space, one inch outside the mid-clavicular line, and was of a heaving character. A thrill could be felt in the aortic area where there was a loud and rough systolic murmur, which was propagated to the neck and towards the right axilla; a systolic murmur was also audible in the mitral region traceable towards the left axillary line. The blood pressure was 100/75 on the right side, and 120/60 on the left. The pulse was markedly anacrotic and of fair volume in the right arm, while in the left it was of a better volume but not anacrotic. The ne...