Low cardiac output is a common problem in the ICU and may be caused by a diverse range of diseases/conditions including: cardiac ischemia, tamponade, pneumothorax, cardiac contusion, hypovolemia and obstructive processes (pulmonary embolus). In order to effectively manage such patient’s one must have an accurate method of measuring cardiac output, an effective method of determining the cause of low cardiac output and finally, methods to empirically treat low cardiac output. The importance placed on measuring cardiac output can clearly be seen in the explosion of new devices designed to more easily, efficiently and frequently monitor this parameter in the intensive care setting.