Twenty seven patients, almost all chronic bronchitic, and with a "chronic cor pulmonale" according to the E. C. G., were followed clinically, radiologically and for E. C. G. and pulmonary functions, and also for the hemodynamics, during a minimum of 3 years, the average length of observation period being about 5 years. Twelve patients died during this observation time. Periods of right heart failure (R. H. F.) were frequent : 3.6 +/- 3.0 in average, slightly more frequent in the deceased patients than in the others. The average delay between the onset R. H. F. and death was of 49.3 +/- 30.8 months ; the survivors on average lived another 54.6 +/- 30.8 months after their first R. H. F. The mean pulmonary arterial pressure (PAP) was quite stable, going from 27.5 +/- 7.0 to 31.2 +/- 9.6 torr (an unsignificicant difference); in only 9 cases did the PAP increase of more than 5 torr during the observation period (acute attacks excepted). The PAP evolution was not significantly different in the deceased and the survivors. PAP worsening by steps after a fit of R. H. F. was observed in only 4 cases. Chronological variations of PAP were well correlated with those of Pao2 during the same period : r = -- 0.68, P less than 0.001. The hemodynamic evolution (PAP), that of the E. C. G. and the volume of the heart were reasonably parallel to the overall clinical evolution ; the E. C. G. evolution had the closest match with the overall clinical evolution (78% of cases). The E. C. G. enables only a late diagnosis of CCP but its evolution is very valuable for prognosis. Hemodynamic tests have a double value initially for diagnosis and later for the evolution.