The heart and the lung make up an inseparable anatomic and functional unit. The changes in one affect the other and vice versa. In acute myocardial infarction a heart failure syndrome develops. This syndrome is characterized by passive pulmonary congestion, which leads to hypoxemia. This hypoxemia indicate the functional disturbance of the lung, and the hemodinamic evolution of the disease. Arterial gases determination is the best way to assess the sickness progression. A certain paralelism exists among the central venous saturation, cardiac insufficiency and the degree of pulmonary disfunction. Such a procedure is not very appreciable and does not substitute the direct analysis of the arterial PO2. The pulmonary complications in the myocardial infarction shock are directly responsable of death in 50% of the patients. To heart failure and shock, hipperfusion and hypoxia are added. Many vessels close due to the decrease in the pulmonary flow. This brings about the release of substances that are toxic to the vessel causing an inflammatory vascular reaction. The decrease in the flow harms the lung cell and for this reason atelectasia or alveolar colapse occur; besides inducing the formation of shunts. Under these conditions the lung compliance decreases. The areas that are badly ventilated and hypoperfused can easily become infected and pneumonitis and abscesses cause even more harm to the tissue. The decrease in the speed of circulation and hematologic changes of shock, induce a diseminated intravascular coagulation. What was stated before leads to an important reduction of the lung as a depurating organ and makes the shock irreversible. As far as therapy is concerned in the prevention of vascular colaps and the improvement of the oxemia, oxygen is very useful when there is a venous congestion (clinically, X rays, and oxemia). When the concentration of O2 is lower than 50% in the cases with slight cardiac failure; do not use oxygen in higher concentrations unless the hypoxia is associated to acute pulmonary edema and shock. Mechanic ventilators, and intermitent possitive pressure are recommended even though they have a posenous effect on the cardiac output. Always keep the air ways permeable: changing position, breathing exercises, humidifications, aspiration of secretions, intubation, or traqueostomy depending upon the various cases.