Two groups of patients of comparable age, one comprising 12 subjects without detectable cardiac disease and the other comprising 38 patients with calcific aortic stenosis (CAS) underwent clinical, electrocardiographic, echocardiographic and haemodynamic studies to assess the degree and significance of left atrial hypertrophies in CAS. The volume of the left atrium (LA) was globally increased in CAS (maximum volume 68 per cent: 26/38) and LA ejection fraction was decreased in 60 per cent of patients (23/38). However, the maximum volume was only moderately greater than that of normal subjects (+38 per cent). The most specific non-invasive investigation for left atrial assessment is echocardiography. There was a linear relationship between LA angiographic volume and echocardiographic antero-posterior dimension (r = 0.43; p less than 1 x 10(-2)). The duration of the P wave in S2 was a specific (75 per cent) but relatively insensitive (27 per cent) sign of LA dilatation in pure CAS. On the other hand, the Morris index based on the surface of the P terminal force in V1 was quite sensitive (77 per cent) but not very specific (25 per cent). The maximum LA volume was not related to left ventricular volume, the severity of CAS, diastolic indices of compliance or left ventricular mass. However, the minimum LA volume (after atrial systole) was related to left ventricular end diastolic (r = 0.35, p less than 0.05) and end systolic volume (r = 0.34, p less than 0.05). The LA ejection fraction was inversely related to mean pulmonary capillary pressure (r = 0.34, p less than 5 x 10(-2).(ABSTRACT TRUNCATED AT 250 WORDS)