Respiratory dysfunction following cardiac surgery is well documented and due in part to the location of the incision and nature of the surgery. Post-operative pulmonary complications (PPCs) remain a significant problem following cardiac surgery, sometimes causing prolonged length of stay in hospital as well as increased morbidity and mortality; with the greater risk to older adults and individuals with obstructive lung disease. Positive expiratory pressure (PEP) therapy is thought to increase lung volumes and facilitate secretion clearance. The purpose of this study is to investigate whether the addition of oscillating PEP therapy to standard postoperative treatment is more effective in decreasing the incidence of PPCs and increasing functional capacity at time of discharge in 'high risk' patients undergoing elective cardiac surgery.