Eight dogs underwent assisted and controlled ventilation with either endotracheal tubes or 14-gauge intravenous catheters inserted into the trachea via the cricothyroid membrane. Cardiovascular and respiratory data were collected and autopsies were performed to assess tissue damage, using gross pathologic and microscopic studies. The data showed no apparent trespass on physiologic functioning. Autopsies displayed trauma to the trachea for both ventilation methods. Transtracheal,ventilation did not cause significant anatomic damage and did not adversely impair the cardiopulmonary function in these dogs.