There is concern among critical care nurses, other health professionals, and the public about the growing number of critically ill patients requiring prolonged mechanical ventilatory support (MVS). These patients consume a disproportionate amount of financial and personal resources burdening both hospitals and families. Past research has focused on the use of point-in-time respiratory and ventilatory measures to predict a patient's success of breathing spontaneously. Until recently, left ventricular (LV) function and the role that it could play in preventing successful weaning from MVS has received little attention. The purpose of this study are to examine the relationship between the presence of heart failure and surrogate indicators of LV function, and to develop a predictive model of the duration of MVS based on indicators of LV function. The specific aims of this study are to determine: (1) the relationship between point in time indicators of heart failure (LV ejection fraction and maximal power), and (2) the relationship between LV function and the duration of MVS. The independent variables are index of heart failure and surrogate indicators of LV function, dependent variable is duration of MVS. The control variables are breathing pattern and health status risk. A prospective, purposive sample of 96 subjects will be obtained from the population of patients who are 18 years of age or older, are mechanically ventilated, had MVS initiated during this hospitalization, have an arterial pH between 7.35 and 7.45, and have a pulmonary artery catheter in place. Potential subjects will be excluded if they do not have neuromuscular integrity. Subjects will be followed weekly from the initiation until they wean, reach 29 days, or die. Analysis will include correlational and survival analytic techniques.