Efferent vagal stimulation in the anesthetized dog with constant ventricular rate caused either no change in coronary sinus outflow and cardiac work, or a decrease in coronary sinus outflow associated with a greater decrease in cardiac work. When the decreases were observed they could best be explained by a negative inotropic effect of vagal stimulation on ventricular muscle, rather than by a direct vasomotor effect of vagal stimulation on the coronary bed. Critical review of apparent divergent results previously reported regarding the effect of vagal stimulation on coronary flow reveals that they are not inconsistent with the above hypothesis.