The hallmark feature of cardiogenic shock is low cardiac output due to the heart's inability to pump effectively. This leads to inadequate tissue perfusion and oxygen delivery despite normal or elevated preload. The primary cause is severe myocardial dysfunction, commonly from acute myocardial infarction. The resulting poor contractility decreases stroke volume and cardiac output, causing systemic hypotension and organ hypoperfusion. Therefore, low cardiac output is the defining hemodynamic characteristic of cardiogenic shock.

Reference: Harrison's Principles of Internal Medicine, J. Larry Jameson, 20th Edition.