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SUMMARY In a series of over 6000 patients referred for fetal echocardiography during an eight year period, 37 fetuses were found to have complete heart block. There were 16 cases of isolated heart block and 21 cases associated with structural heart disease. All mothers of fetuses with isolated complete heart block had evidence of circulating syndrome Sjogren A antibody (Ro). Only one mother had clinical evidence of connective tissue disease. In the 21 cases associated with structural heart disease there were 17 cases of atrioventricular septal defect, one case of secundum atrial and perimembranous ventricular septal defects, two cases of tetralogy of Fallot, and one case ofpulmonary stenosis. All fetuses with atrioventricular septal defects and complete heart block had left atrial isomerism. Additional abnormalities of the great arteries were often found in this group; these were double outlet right ventricle, transposition of the great arteries, pulmonary atresia, coarctation of aorta, and stenosis of the pulmonary or aortic valves. Intrauterine congestive heart failure was a feature of four cases in the group with isolated complete heart block and 1 1 cases of the group with associated structural heart disease. The outcome in the fetuses with isolated complete heart block was better than in those with heart disease: 12 of the 16 fetuses are alive, two of them have a pacemaker. But only three ofthe group of21 fetuses with cardiac malformation are alive, and two of them have a pacemaker.Complete heart block was first described as "impaired atrioventricular syndrome" by Morquio in 1901.' The condition was characterised by a slow pulse, syncopal attacks, and sudden death. Since then many workers have reported cases of isolated complete heart block and its association with structural heart lesions.' Hull et al in 1966 recognised the relation between maternal systemic lupus erythematosus and complete heart block; they described a child born to a mother with active lupus.' More recently a strong association has been found between isolated infantile complete heart block and the presence of syndrome Sjogren A antibody in maternal serum.67 This antibody is also known as Ro, after the patient in whom it was first detected.8The first case of fetal heart block was reported by Plant and Steven in 1945.9 The diagnosis was suspected by fetal heart auscultation and fetal electrocardiogram. Fetal heart block can now be detected by M mode and Doppler echocardiographic examinRequests for reprints to Dr

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The ability to measure aortic valve area clinically has emphasized the need to understand the changes in aortic valve orifice area during flow. To compare the performance of normal and stenotic human aortic valves we used a pulsatile flow model that simulated in vivo flow conditions. Five normal autopsy specimens and 15 stenotic valves removed at operation were mounted into the model. Valve function was assessed by analysis of video recordings of valve leaflet motion during flow. Over the flow rates tested normal valves demonstrated a linear increase in orifice area. There was no resistance to leaflet opening and valve closure was rapid. The majority of stenotic valves demonstrated an increase in orifice area at low flow rates. No valve showed any increase in maximal area beyond flow rates of 3 l min-1. Increased leaflet resistance of these abnormal valves resulted in notably slower opening and closing rates. In patients with a high cardiac output and severe stenosis, overestimation of the anatomic orifice area derived by the Gorlin equation can result. This is not related to variability in maximal orifice area.