To analyze the left atrial (LA) systolic function, LA dimension (D) obtained by aortic root echograms and LA pressure (P) by a Millar's catheter tip manometer were recorded simultaneously in 32 patients (pts) in regular sinus rhythm [7 normal subjects, 7 pts with hypertension, 8 pts with old myocardial infarction, 3 with angina pectoris, 3 with congestive cardiomyopathy, 1 with hypertrophic cardiomyopathy, 2 with mitral regurgitation, 1 with mital regurgitation with stenosis]. The pressure-dimension relation of the LA was composed of two loops