Hello! Thank you for asking on HCM! I understand your concern and would like to explain you that Marfan syndrome is one of the many fibrillopathies (connective tissue disorders), that affects many body organs including aortic wall structure. Aortic wall consistency may be damaged, manifested with aortic dilatation and aneurisms, sometimes leading to aortic wall dissection. Thus, it is of utmost importance to follow up aortic dimensions and structure, in order to be right in time for any needed intervention. Facing your actual aortic diameter, seems that it is around the upper limit of normal. So, you have to be very careful with your hypertensive therapy. Beta-blockers (Atenolol) are the main stay of therapy. You have to follow your doctor advice to start Losartan even at a higher dose, if it is judged necessary for controlling blood pressure. Yo may try other anti-hypertensive medications as well (always under medical advice and supervision). If aortic diameter increases more than 50-55 mm, despite appropriate therapy, then a strict supervision for a near and potential aortic surgery would be necessary (to avoid a fatal aortic dissection and rupture). Hope to have been helpful. Greetings! Dr. Iliri