Objective: To investigate the heterogeneous response to β blockade in patients with Marfan syndrome by non-invasive assessment of the aortic pressure-area curve. Design and patients: 25 patients with the Marfan syndrome who used β blocking agents (mean (SD) age, 29 (10) years; 20 men, five women), seven without β blockade (34 (14) years; five men, two women), and 10 controls (29 (5) years; seven men, three women) underwent magnetic resonance imaging and non-invasive continuous blood pressure measurement. Pressure-area curves were constructed at the level of the descending thoracic aorta. A transition point was defined as the pressure at which the pressure-area relation deviated from its elastic (linear) to the collagen (exponential) course. Setting: Tertiary referral centre for adult congenital heart disease. Results: In six patients (five with and one without β blockade), a transition point in the pressure-area curve was observed, indicating that the load bearing component was not only elastin but also collagen. In the remaining 26 Marfan patients and in the control subjects a linear pressure-area relation was observed. Conclusions: This new non-invasive method to derive aortic pressure-area curves showed that most patients with Marfan syndrome have a similar pressure-area curve to controls with similar blood pressures. Five patients on β blockade showed a transition point in the pressure-area curve which could play a crucial role in the heterogeneous response to β blocker treatment in Marfan patients. Patients with a transition at low blood pressures may not benefit from β blocking agents.