Hello Rule Rattray,
This is a question you really should ask your doctor. As you know well, Viagra, Cialis and Levitra are not recommended for patients who are being treated for heart conditions because of drug interaction. Online sites are great for getting the information you need to manage your care, but can not take the place of your doctor's advice and care.
Even though you have had bypass surgery, it is possible that you are not a candidate for Viagra for reasons other than the obvious one about taking too much vasodilator. It is possible you will be a candidate for using viagra, as the warnings all pertain to men who are taking nitrates for heart conditions. You can read about that here. This is where it is best to let your doctor discuss this with you and make the decision then.
Take care and stay in touch. Let us know how you are doing!Vicki M