I'm not a cardiologist, but from what little cardiology I've studied, it could have also been a matter of a lack of collateral circulation. This sometimes leads to fatal heart attacks in pre-geriatric athletes. I'm not aware of any cardiac related risks in MS patients who stay physically active, and not aware of any cardiac risk factors from MS medications other than a hypertension risk from corticosteroids use. Remember as well, heart attacks have a huge genetic factor. Ed Burke being a sad example of this, who was in amazing condition and had a fatal heart attack while cycling. Anyway, Sheldon is such a tragic loss. My prayers are with his family and friends.