This video is very interesting. I am going to read Dr. Cowan's book.
He says the heart can't possibly be the pump we think it is.
The walls of the blood vessels would have to be thicker.
There must be other means, local means, to pump blood in the body where it needs to move.
I am still watching this but recommend it. Dr. Cowan is a former ER physician, an MD and seems to be an open minded person who is very good at explaining concepts.
I have posted some messages tangentially concerning this topic. From the view of a new physiological paradigm. The "mammalian stress mechanism" theory inherently describes this aspect of the heart not being a pump.
You Tube Slide Shows
I don't know how this can be so completely unknown (judging from the youtube view counts) because it is extremely rational concept 100% in agreement with latest research (some of which authored by the person running the website).