The effect of opening and closing the infrarenal arteriovenous (A-V) fistula on left ventricular (LV) function was analysed in 12 anaesthetised dogs, instrumented with a micromanometer and a pair of ultrasonic crystals for measurement of LV diameter (D). Plasma noradrenaline (NA) levels sampled from the right ventricular cavity were determined using a high-performance liquid chromatographic method. Immediately after opening of the A-V fistula, the peak LV pressure (P) decreased by 4.3 kPa from the control value of 14.4 kPa and returned to the control level within 30 s. End-diastolic diameter did not significantly change immediately after opening the fistula but then gradually augmented to 28.3 mm, at the stable stage 5 min later. End-systolic diameter was significantly reduced from 22.0 to 20.8 mm immediately after opening and remained reduced until the fistula was closed. The percentage shortening of the LVD increased from 17.1 to 20.1% with the initial fall in LVP, and continued to increase to 26.6% with subsequent enlargement of diameter. With closure of the fistula, a directionally opposite response was observed. The end-systolic P-D relation, obtained by superimposing the series of loops and plotting end-systolic pressure against end-systolic diameter, fell on the single function curve during the initial pressure change, and clearly shifted to the left during the stable stage of volume loading and returned to the control relation with closure of the A-V fistula.2+ leftward shift of the end-systolic P-D relation during the stable stage of volume loading.(ABSTRACT TRUNCATED AT 250 WORDS)