Background: Adult patients with cystic fibrosis (CF) have resting abnormal large artery haemodynamics. Here, we obtain further insight in patients with CF by evaluating haemodynamic response to physiological stress. Methods: Thirty-six stable CF patients mean (SD) age 28.9 (9.0)years and 25 controls matched for age, gender and body mass index were studied. Central haemodynamic parameters; including augmentation index (AIx) and wasted left ventricular pressure energy (Delta E(w)) were determined pre, during and post light intensity cycle ergometry. Results: During exercise, despite a similar heart rate and blood pressure, patients had comparatively greater Delta E(w) (P=0.03) and trend towards greater AIx (P=0.07) than controls. Exercise Delta E(w) was greatest in patients with CF related diabetes (n=11). In all subjects, exercise Delta E(w) was related to age (r=0.54, P <0.001) and FEV(1)% predicted (r=-0.32, P=0.01). Conclusions: Adults with CF have an abnormal haemodynamic response to exercise. This finding has deleterious implications for myocardial performance.