The interventricular septum was studied by biventricular angiography in 52 patients divided into 4 groups: the first group consisted of 14 normal subjects; the second of 10 patients with hypertension (9 cases) or aortic stenosis (1 case); the third, of 19 patients with echocardiographic asymmetric septal hypertrophy, and the fourth, of 9 cases of cardiomyopathy with dilatation. The following parameters were measured: septal thickness at 4 different points and mean septal thickness, the height (long axis) and surface of the septum in diastole and systole. The percentage variation was calculated. There were no significant differences between Group I and II; there was a significant difference (p less than 0,01) in the variations of septal thickness of the upper segments between Group I and III. This difference remained significant (p less than 0,05) for the variations of mean thickness between Group I (-38%) and Group III (-18%). There was also a significant difference (p less than 0,05) in the variation of height between Group I (23%) and Group IV (9%). None of the variations of septal surface reached the threshold of statistical significance between the four groups. Biventricular angiography can therefore demonstrate certain abnormalities of septal motion. In asymmetric septal hypertrophy, the variations in thickness are significantly less pronounced than in normal subjects but the motion in the longitudinal axis does not differ significantly. In cardiomyopathy with dilatation, however, the variation in septal height is the most affected parameter.