Brain death-related hemodynamic instability may preclude donor heart procurement. The relationships between the initial changes of myocardial workload, hemodynamic deterioration, and myocardial histological changes caused by acute induction of brain death are unclear. Cats (n = 15) were submitted to brain death by rapid inflation of an intracranial balloon. A further 12 cats served as a sham-operated control group. The changes in heart rate, mean arterial blood pressure, systolic and diastolic arterial blood pressure, left ventricular developed pressure, LV dP/dtmax, rate-pressure product (RPP), and circulating noradrenaline and adrenaline were studied during 240 min after the induction of brain death. Central venous pressure was kept constant. The hearts were histologically examined afterward. Electrocerebral activity disappeared within 30 sec after balloon inflation. At 3 min, noradrenaline and adrenaline levels had increased 75- and 40-fold, respectively, compared to pre-induction levels. The hemodynamic response was characterized by an early and rapid increase of hemodynamic variables at 2.9 +/- 0.2 min. This was followed by a second phase of normalization or deterioration. Two distinct subgroups (n = 9) became hemodynamically unstable (HDU), characterized by a systolic arterial blood pressure < 90 mm Hg, at 108 +/- 29 min, and progressively deteriorated to 67 +/- 8 mm Hg at 240 min after inflation of the balloon. The hemodynamic variables of the other, hemodynamically stable (HDS), subgroup (n = 6) normalized at 60 min after inflation. Hemodynamic deterioration of the HDU subgroup compared to the HDS subgroup was significant at 10 min after induction of brain death. The maximum values of RPP were similar in the two subgroups. Respiratory and metabolic variables at the end of the experiment were not different in both subgroups. Histological evidence of myocardial damage was present in 73% (11/15) of the brain dead cats and absent in the control group. The histological changes were identified both in hearts of HDU (6/9) and HDS (5/6) cats. In the cat, no relationships were demonstrated between the acute increase of myocardial workload, the occurrence of hemodynamic deterioration, and myocardial histological changes after rapid induction of brain death. These results may contribute to the discussion whether hemodynamic instability of the donor is an appropriate exclusion criterion for heart transplantation.