Hi Thanks for posting on HCM Dizziness while walking is usually caused by a circulatory problem called orthostatic hypotension or postural hypotension.This condition could be caused by Dehydration, Heart problems, Endocrine problems, After eating meals, Nervous system disorders. With a history of sugery for coarctation of the aorta, cardiovascular complicatioons like High blood pressure, Enlargement in a section of the wall of the aorta, Premature coronary artery disease...are common and may give you such symptoms. I will suggest you try the following: -Eat small meals -Get plenty of fluids -Exercise your calf muscles before sitting up -Avoid bending at the waist -Wear compression stockings or abdominal binders -Get up slowly -Elevate your head in bed If symptoms persist with these measures, you see your Doctor for examination and possible drugs for this condition like fludrocortisone, midodrine. Hope this will help Wish you good health