The degree of pulmonary congestion seen on chest radiographs taken in the intensive care unit was compared with the end-diastolic pulmonary artery pressure in 65 patients with recent transmural myocardial infarcts without cardiogenic shock. There was good correlation between the radiographic appearances and the end-diatrolic pulmonary artery pressure, so that the severity of left heart insufficiency could be diagnosed radiologically at an early stage. Errors were due to the time interval which must pass before the radiographic appearances approximate the haemodynamic changes. This resulted in a diagnostic "phase lag" (following a rise in end-diastolic pulmonary artery pressure) or in a post-therapeutic "phase lag" (after a fall in end-diastolic pulmonary artery pressure). Repeated examinations allow one to recognize changes in the haemodynamics. One should pay particular attention to the features of pulmonary venous and pulmonary arterial hy