This chapter examines the interaction of a new formulation containing the following ingredients: methylene chloride; ethanol; propane; butane and isobutane. The last three are hydrocarbon propellants contained in mixture A-46. Experiments were carried out on adult mongrel dogs of either sex weighing between 13 and 24 kg, anesthetized with intravenous injection of 30 to 35 mg/kg of pentobarbital sodium. The myocardial and hemodynamic effects of A46, methylene chloride, and ethanol were studied in the open-chest dog preparation. Administered separately or in various combinations, these compounds attenuate myocardial contractile force as well as cardiac output. The decrease in cardiac output under the influence of A-46 overshadows that of methylene chloride when both are administered simultaneously. Some degree of antagonism on systemic blood pressure between A-46 and ethanol was observed. Ethanol administered in concentrations of 5%, 7.5%, and 10% combatted the arrhythmogenic effect of methylene chloride.