The positive inotropic action of hexamethonium in hypodynamic and freshly prepared papillary muscles of the eat and the hypodynamic heart-lung preparation of the dog has been demonstrated. Within certain limits, there exists a proportionality between the concentration of hexamethonium and the magnitude of the inotropic response. In both preparations results have been obtained which indicate that a state of partial refractoriness to the positive inotropic action of hexamethonium may be produced.