Brucine

Arthur Bishop (Bronson) was obviously aware of this poison when Steve mentioned what was ailing him at the end. Apparently, this poison makes it look like someone dropped dead from a heart attack. Instead of the elaborate scheme at the beginning with the pilot light, drugged tea, and a flammable book ignited by a bullet, why not just coat the teabags with brucine and be done with it? Now, I do like the film and thought the beginning was terrific. Still, it makes no sense that if you have access to a hit's domicile that you'd do anything but a quiet poisoning.