One of my many reasons for not considering this mechanism to be programmed by
someone is implied in this thread:
Message 1 Distinguishing Designs
Others have given similar reasons as:
We have a well understood mechanisms for producing the appearance of design in biological (or any imperfectly replicating things) organisms.
When we examine potential designs we see them falling into very, very different and easily distinguishable categories (the point of the above referenced thread). The heart like other biological components falls very clearly into the not designed category.