In 4 7 a nima ls (rats, rab bits) the cardiac side effects of prolonged (3 to 6 hours) abdomi nal aortic cross-clamping and unc lam ping (3 to 6 ho urs) were in vestigated. T he rela tive insta ntaneous ventricu lar vascular vo lume (IVVV), a factor refl ect ing myoca rd ial b lood supply and t he rate p ressure product lAPP) represe nti ng myocardia l oxyge n dema nd were used as para mete rs. Fo llowing cross-clampi ng the IVVV showed an initia l dec rease while the myocar dial oxygen demand revealed a sudde n increase. Afte r unclamping, the myoca rdial oxygen demand dec reased and IVVV improved. Minimal levels of both IVVV and RPP occu rred at 6 hours following unc lamping. This may be an effect of a myocardial inhib iting substance, released by ischemia and necrosis of the lower e xtremity. Keyword s: Abdomi nal ao rtic cross-clampi ng-Myocardia l oxygen dema nd-Instan taneous ventricular vascu lar volume-Ra te pressure product