PURPOSE--To analyse the influence of mannitol added to Krebs-Henseleit (KH) solution on the myocardium edema and myocardial function. METHODS--Isolated rat heart under isovolumetric contractions studied according to Langendorff's technique were perfused with KH solution at constant flow during 90 min. The coronary perfusion pressure, diastolic and systolic pressures were recorded at every 15 min. At the end of the experiment, myocardium water content was measured in hearts perfused with KH solution (group I, n = 9) and in hearts perfused with KH solution plus 8mM mannitol (group II, n = 8). These results were compared to non-perfused control heart (n = 9). RESULTS--Myocardial water content was statistically higher in group I (80.8 +/- 1.3) compared to group II (78.1 +/- 0.7) and control group (75.5 +/- 0.5). Systolic arterial pressure was statistically higher in group I (86.2 +/- 11.5mmHg) compared to group II (72.7 +/- 21.1mmHg). There was no difference in the diastolic pressure between the two groups. Coronary perfusion pressure (Pp) increased progressively during the experiment in both groups. However, Pp was lower in group II than in group I. CONCLUSION--Mannitol added to KH solution significantly attenuates the myocardium edema in the isolated perfused rat heart.