Balloon flotation catheterization of the central circulation provides data which may be most meaningful and important to the management of critically ill patients. It allows the measurements of the filling pressures of the right and left ventricle as well as the cardiac output. These data combined with information concerning cardiac rhythm, heart rate, arterial pressure and other variables place the principal determinants of cardiac function at the disposal of the critical care personnel. In particular, the physician may optimize left ventricular filling pressure and then alter other functional determinants of cardiac performance so as to optimize the relationship of cardiac output to the metabolic needs of the body tissues and systems. Continued hemodynamic monitoring also provides prompt objective information as to success or failure of therapeutic interventions. It thereby allows for the most rational decision making and effective alteration in the therapy applied to the individual critically ill patient.Much still needs to be done to establish completely the impact of such monitoring techniques upon patient management. However, experience thus far has been most promising. Large numbers of physicians and health care personnel now rely on pressures provided by the pulmonary capillary wedge pressure in their decisions about fluid therapy. Others are rapidly assessing the importance of the cardiac output and other parameters of cardiac function on a semi-continuous basis.Thus, balloon flotation catheterization has allowed the application of sound physiological principles to the understanding of circulatory abnormalities characterizing important patient illnesses and provides a rational basis for the selection of therapy with objective quantitative assessment of responses. The procedures are simple; the complication rate is low, and the information provided is highly relevant to clinical practice.