It has been postulated that near-drowning in fresh water may cause hemodilution and hypervolemia due to the hypotonicity of the aspirated water. In contrast, near-drowning in seawater, because of its hypertonicity, may lead to hypovolemic shock. We evaluated the hemodynamic effects of the instillation of 20 mL/kg of solutions of various tonicities (sterile water, 0.225% sodium chloride, 0.45% sodium chloride, normal saline, 2% sodium chloride, and 3% sodium chloride) into the lungs of anesthetized dogs and compared the results with those for control animals who were made anoxic for five minutes. There was no difference in the hemodynamic effects of hypotonic, isotonic, or hypertonic solutions when compared with anoxic controls. There was an immediate fall in cardiac output and increase in pulmonary capillary wedge pressure, central venous pressure, and pulmonary vascular resistance, regardless of the solution, which was statistically the same as the changes in the anoxic controls (P greater than .02). Likewise, the effective dynamic compliance of the lungs decreased precipitously, was indistinguishable between solutions, and was not statistically different from the anoxic controls (P greater than .10). The pulmonary capillary wedge pressure and central venous pressure peaked at ten minutes and then declined gradually over four hours independent of the tonicity of the aspirated fluid. The cardiac output and effective dynamic compliance of the lung dropped rapidly and remained depressed throughout the experiment, and the pulmonary vascular resistance gradually worsened throughout the four hours of study. Similar results occurred with the anoxic controls. The cardiovascular changes that occur with near-drowning and aspiration of water are not dependent on the tonicity of the aspirated fluid but are the direct result of anoxia.