A retrospective study of 100 cases of obstructive cardiomyopathy of the left ventricle has allowed us to predict a mean survival of 30 years after the murmur has been discovered. A comparative angiographic and haemodynamic study was carried out on 50 cases using the NYHA classification into four functional stages. The lowering of functional status, at rest, seems to occur: -With the advent of a permanent intraventicular gradient (6 +/- 5 mmHg in stage 56 +/- 38 mmHh in stages III and IV, p less than 0.001). Despite preservation of the indices of contractility (VECmax 1.81 +/- 0.66 c/s at stage I, 1.71 +/- 0.7 C/S at stages III and IV). -With a progressive change in the ventricular complicance (dV/dP/VTD 0.029 +/- 0.016 at stage I, 0.017 +/- 0.01 at stage III and IV). A progressive change in venticular complicance seems to be secondary to an increase in the parietal diastolic thickness and to lesions visible histologically. It governs the natural history of the condition and the results of surgical treatment.