The peak systolic wall stress at the equator of the left ventricle (sigma max) is the maximum load that the myocardial fibres bear during contraction. It is an index of the adaptation of the left ventricle to cardiac disease, and, when elevated, it indicates cardiac decompensation. sigma max was calculated by coupled M mode echo-LV pressure recordings in 51 cases: 11 patients without LV disease, 14 patients with aortic stenosis (AS), 14 patients with aortic incompetence (AI), 7 patients with severe mitral incompetence (MI) and 5 patients with cardiomyopathy with dilatation (CMP). sigma max was calculated from Mirsky's formula, the length of the long axis being deduced from the short axis and the diastolic:systolic ratio of these two axes from ventriculography. The normal value of sigma max by this method is 220 dynes 10(3)/cm2 +/- 30 with an upper limit of normal of 280 dynes 10(3)/cm2. sigma max was normal in patients with AS and AI, and increased in the cases of MI and CMP, in positive correlation with LV volume (r = 0,47) and the shape of the LV (long:short axis ratio). No correlations were found between sigma max and maximum LV pressure. The relatively low values of sigma max compared to the results obtained from coupled echo-angio recordings are partly due to the thick walled LV model and, to a large extent, to the lower values of short axis when measured by echo compared to angiography.(ABSTRACT TRUNCATED AT 250 WORDS)