In order to investigate the relationship between left atrial pressure and volume, left atrial echograms and mean pulmonary wedge pressure were obtained on 64 patients with various cardiac diseases. A statistically significant relationship was found in the whole group (r = 0.67, p < 0.01), but there was a considerable degree of dispersion around the regression line. A good correlation was present in 6 patients with hypertrophic cardiomyopathy (r = 0.97, p < 0.01) and in 13 patients with long standing mitral valve disease (r = 0.85, p < 0.01). There was no correlation in coronary artery disease patients.