Simultaneous chest X ray, pulmonary capillary wedge pressure, and pulmonary artery oxygen saturation measurements were obtained in 30 patients with acute myocardial infarction. The severity of radiologic abnormalities generally correlated well with pulmonary capillary wedge pressure. Serious misinterpretation of left ventricular failure by X-ray criteria, although uncommon, occurred in the presence of "preclinical" failure, hypoxemia, or posttherapeutic phase-lags. Individual radiologic criteria of left ventricular failure appeared in a predictable sequence. Redistribution of flow appeared early, followed by loss of the sharp marginal contour of the pulmonary vessels, development of perihilar haze, and, finally, periacinar rosette formation. Thus, radiologic criteria of the degree of pulmonary vascular congestion, when related to pulmonary capillary wedge measurements, provide a basis for consistent and rational therapy of left ventricular failure secondary to acute myocardial infarction.