I have aortic stenosis and am wondering if nitric oxide is safe for me as a workout supplement. ?

NO!!!!!: If you have severe aortic stenosis, heavy workouts may be unsafe and supplements may be extremely unsafe.

Aortic stenosis: I would recommend you get your guidance from a board certified cardiologist familiar with you case. Preferably they would have access to your history, exercise tolerance, and most recent echocardiogram and would be able to risk stratify you not only for your recommended exercise regimen but also any supplements you may consider taking, especially those that affect bp. As can be serious.

Unwise: Typically, "nitric oxide" is l-arginine powder. L-arginine is a precursor of nitric oxide. Nitric oxide is released from the endothelium and causes vasodilation. There is no proven performance advantage for taking l-arginine before training or competitive exercise. Arginine supplementation is unlikely to create greater vasodilation, but if it did, this could be dangerous in aortic stenosis.