Objective:To evaluate and compare the factors associated with pulmonary edema in cardiac tamponade and myocardial ischemia.Design:Prospective, controlled laboratory study.Setting:Animal research laboratory of a university hospital.Subjects:Fourteen anesthetized dogs.Intervention:Extravascular lung water (EVLW) was measured with thermal indocyanine green dye double-indicator dilution method and hemodynamic indices were determined by the pulmonary artery flotation catheter. Seven dogs were used in the tamponade model, and seven other dogs were used in the myocardial ischemia model. Furthermore, ten dogs were dedicated to measure plasma colloid osmotic pressure (COP) and blood gas analysis during cardiac tamponade and myocardial ischemia.Measurements and Main Results:Mean right atrial pressure (MRAP) (7→10 mm Hg), pulmonary capillary wedge pressure (PCWP) (10→13 mm Hg), and EVLW (5.4→10.1 mL/kg) increased during tamponade, but all of these indices returned to the control level after release of tamponade (MRAP, 7 mm Hg; mean PCWP, 11 mm Hg; mean EVLW, 5.2 mL/kg). Myocardial ischemia caused increases in PCWP (10→14 mm Hg) and EVLW (5.6→9.6 mL/kg). Although PCWP returned to the control level, EVLW remained elevated (9.2 mL/kg) after reperfusion. EVLW had good correlations with MRAP (r2= .64,p< .05) and PCWP (r2= .62,p< .05) during cardiac tamponade. Despite a fair correlation between EVLW and PCWP during ischemia (r2= .73,p< .05), EVLW was not related to PCWP after reperfusion. COP decreased during myocardial ischemia and at the reperfusion period, but there was no significant change in COP in the cardiac tamponade model.Conclusions:In contrast to a close relation between hydrostatic pressure and EVLW in cardiac tamponade, hydrostatic pressure was not a determinant of pulmonary edema during the reperfusion period after myocardial ischemia.