1. A method, comprising: delivering a heart failure therapy, including stimulating a vagus nerve and avoiding physiological habituation to stimulating the vagus nerve, wherein: stimulating the vagus nerve includes non-selectively stimulating both afferent axons and efferent axons in the vagus nerve using a stimulation signal having a plurality of modifiable stimulation parameters, wherein the modifiable stimulation parameters include at least one modifiable neural stimulation schedule parameter; and avoiding physiological habituation includes stimulating the vagus nerve according to a stimulation schedule independent of heart rate, and limiting modification of the at least one neural stimulation schedule parameter using a programmed limit for allowed modifications to the at least one modifiable neural stimulation schedule parameter.