1. 1.

    The influence of perfusion pressure on stroke volume and heart rate was examined in the isolated ventricle. Input pressure, within the physiological range (10–20 cm of water), had a direct effect upon stroke volume and heart rate. Output back pressure had an inverse effect upon stroke volume and no effect upon heart rate.

  2. 2.

    Sites that could vary input pressure were investigated by selective denervation in the whole animal. The results indicated that the efferent branchial vessel and auricle may be involved, as well as the branchial hearts and lateral venae cavae.

  3. 3.

    It is proposed that the pressure of venous blood has a limited effect upon ventricular output in vivo.

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