Though drugs such as sildenafil(VIAGRA) and tadalafil are very effective in the treatment of erectile dysfunction, I suppose that you will be taking nitrate tablet for your cardiac problem as you have undergone triple bypass. You cannot take these drugs as dangerous side effects may occur so the drug alprostadil may be suitable to you. Alprostadil is available in injectable, pellet and cream formulations; the drug should be injected into the muscles of the penis or drops of a cream should be inserted into the meatus of the urethra. Other modolities treatment available are: vaccum constriction device, penile prostheses and vascular reconstruction surgery.