This study will include 124 patients over 18 years of age, suffering of acute cardiogenic pulmonary edema, with a respiratory rate greater than 25 bpm and oxygen saturation less than 90 %. The patients will be include just after the beginning of the episode, in prehospital mobile intensive car unit (SAMU) and will be all admitted in resuscitation area in a central hospital. They will be randomly assigned to CPAP or conventional oxygen therapy. The randomisation sequence is generated by the random numbers table. Closed envelopes containing the allocated treatment will be stored in the emergency department and will be opened when the patient is included.