Detection of acute cardiac dysfunction and differential diagnosis of low cardiac output syndrome is challenging for emergency physicians. For the critical ill patient it is essential to rapidly identify the underlying disease to initiate the correct therapy and optimize patient outcome. Echocardiography is the diagnostic tool of choice for the evaluation of low cardiac output states. In the setting of the emergency department the use of focused echocardiography instead of detailed echocardiographic studies of cardiologists is appropriate and should be provided for emergency care. The differentiation in preserved versus reduced left ventricular ejection fraction as a first assessment is helpful, particularly for physicians not well trained in echocardiography. The structured and focused approach to evaluate or exclude differential diagnoses of cardiac dysfunction is the key for optimal management of acute and critically ill patients with low cardiac output.