Until recently, fluorocarbons were the major propellants used in the aerosol industry. However, the potential health hazards associated with the use of fluorocarbons and other considerations have made it necessary to develop aerosols using hydrocarbons as propellants. The propellant mixtures consisting of propane, butane, and isobutane described from 1966 to 1970 are becoming important because they represent a means of continuing to use aerosols without fluorocarbons. This chapter describes an investigation to determine whether the mixture of the three hydrocarbons is more toxic than each of the individual components. The inhalation of the hydrocarbon propellant mixture A-46 in the anesthetized open-chest dog preparation brought about the following hemodynamic changes: a) decrease in myocardial contractility, b) decrease in cardiac output, and c) decrease in left ventricular pressure and systemic blood pressure. With the hydrocarbon propellant mixtures, there is no potentiation of the individual effects of isobutane, butane, and propane.