This case presented the scenario of a patient who had severe bronchospasm from an unknown etiology. Further, she had difficulty speaking and denied any past medical history, which made a diagnosis more difficult. Prehospital providers were challenged with determining the differential diagnosis for bronchospasm and hypoxemia. Was the patient experiencing an anaphylactic reaction, acute asthmatic attack or something else? The key here, once again, is conducting a thorough assessment and patient history. Remember, all that wheezes is not asthma; therefore, providers in this case had to determine if the patient was suffering something such as anaphylaxis, asthma, bronchitis, pneumonia or even congestive heart failure (CHF). Typically, anaphylaxis and asthma affect ventilation, not oxygenation, so until the late stages of anaphylaxis or asthma, the patient will have difficulty moving air, but will be oxygenating OK. We understand that many respiratory conditions can cause wheezing, but CHF? Yes: As left ventricular function diminishes and leads to increased pulmonary pressure, serum begins to leak out of the pulmonary vessels and into the interstitial space. As the interstitial pressure increases, it causes narrowing of the bronchioles, and air traveling through the narrowed bronchioles causes the wheezing sound. Fluid may also be leaking out of the pulmonary capillaries and occupying space in the alveolar sacs. When the interstitial pressure is high and the bronchioles continue to narrow, providers may initially hear only the wheezing and not the crackles from the smaller airways. In these conditions, oxygen is not exchanged adequately into the blood, and the patient becomes hypoxemic. Good assessment and patient history will guide the EMS provider to the cause of bronchospasm. For example, does the patient have a history of asthma? If yes, asthma is likely to be the cause. Does the patient have any rash, hives or swelling? If yes, anaphylaxis is likely the cause. Is the patient elderly, and does he/she show pedal edema, JVD, hypoxemia and/or distended neck veins? If yes, CHF may be the cause. [table: see text] There are questions regarding the use of bronchodilators in patients suffering CHF. If a CHF patient is wheezing (bronchospasm), then a beta-2 selective breathing treatment may be appropriate, along with nitrates and diuretics. Oxygenation is the critical problem in CHF, and hypoxemia will continue to worsen cardiac function. Remember, both bronchoconstriction and alveolar sacs filling with fluid will impair oxygenation of the RBCs and ultimately the vital organs. Focused prehospital management of CHF is aggressive in restoring oxygenation. For example, many agencies are now using oxygen, nitrates, ACE inhibitors and CPAP. By better understanding the pathophysiology of respiratory emergencies and their differential diagnosis, we will improve patient outcomes.