To decide whether distension of the urinary bladder reflexly affects the left ventricular inotropic state, experiments were performed in eight dogs anesthetized with pentobarbitone. After cannulation of both ureters the urinary bladder was repeatedly distended through a urethral catheter with warm Ringer solution at a steady intravesical pressure. The maximal rate of rise of left ventricular pressure (dP/dtmax) obtained at constant heart rate and cardiovascular pressures was used to assess changes in left ventricular inotropic state. Arterial blood pressure was prevented from changing by a pressurized reservoir containing warm Ringer solution and connected to the femoral arteries. Following prevention of the reflex increase in heart rate by atrial pacing, distension of the urinary bladder always increased the maximal rate of rise of left ventricular pressure in the eight dogs. There were no significant changes in left ventricular systolic or end-diastolic pressures. The increase in maximal rate of rise of left ventricular pressure was abolished following the administration of propranolol. The results indicate that a reflex increase in left ventricular inotropic state occurred in response to distension of the urinary bladder. This reflex response involved beta-adrenergic stimulation.