 Failure to wean from mechanical ventilation failure to get the patients off the breathing machine is associated with prolonged stay in the intensive care unit and increased risk of death. Some patients have difficulty successfully getting off the ventilator and breathing on their own. Usually this difficulty is due to lung problems. But sometimes it is due to heart problems, or heart failure. To improve a patients chances of successfully getting off the ventilator early, it is helpful to the doctors to know if patient has heart failure and to measure how severe. With the new monitoring system being studied here, doctors may be able to detect and measure heart failure more easily. 