1. An in vitro preparation of the intact heart of the frog Rana esculenta was set up. 2. The isolated heart, perfused at constant pressure, was spontaneously beating and able to generate physiological values of output pressure, cardiac output, ventricle work and power. It showed the typical phenomenon of the "hypodynamic state" after a relatively constant time from the onset of the perfusion. 3. Perfusion with air-saturated saline and 99.5% oxygen-saturated saline did not show significant differences in the recorded parameters. 4. This experimental model represents a useful tool for physiological and pharmacological studies, especially when the direct analysis of the effects of hormones, mediators or drugs requires an intact heart preparation.