A right cardiac catheterism with a calculation of cardiac output by thermodilution method has been achieved on 40 chronic respiratory failure patients with acute outbreak. The results have been analysed according to the type of chronic pulmonary disease, obstructive (n = 24) or restrictive (n = 16), the number of out asphyxic outbreaks and the necessity of mechanical ventilation (VA). The mean pulmonary arterial pressure (PAP) is high (6.38 +/- 1.58 KPa) systolodiastolo gradient increases with the number of outbreaks (p less than 0.001). The cardiac index is low (2.32 +/- 0.57 1.mn(-1).m2(-1)) and the pulmonary capillary pressure (PCP) is high, specially during the obstructive syndromes. A high level of PAP during mechanical ventilation seems to be of poor prognosis. The authors compare these results to the literature.