 A new monitor Vigileo TM that is connected with a specific cable Flo-TracTM to a catheter that is inside the patients artery arterial line has lately been developed. This monitor can estimate the amount of blood that the heart is pumping per minute, known as cardiac output. The heart is supposed to pump blood harder when a patient is being weaned from the breathing machine. With the above mentioned monitor, we hope to detect those patients whose hearts are weak and are not pumping as hard as they should. 