The heart exhibits right to left communication between the fibres of the muscular part of the interventricular septum.

1900 years ago Galen stated that blood seeps through the perforations in the interventricular septum. However, William Harvey, working 400 years ago, failed to find any. In this study an aqueous solution of a black dye was gently pumped by hand into the right ventricle of 20 porcine hearts. The area in the middle ofthe left muscular part of the interventricular septum in 13 of the hearts was bloodstained under the endocardium at the time the heart stopped beating. The same area of all 20 hearts eventually became stained black. A small amount of black dye seeped through the endocardium of 18 hearts in the middle of the left muscular part of the interventricular septum. In another 20 porcine hearts theinterventricular septa were dissected after boiling. The deep pit under the anterior interventricular sulcus communicated with the right ventricle and with the middle of the left muscular part of the interventricular septum between the fibres of the muscle. The communication closed tight at the very early systole. The communication resembled that reported by Galen 1900 years ago. The communication may be the real foetal route for diastolic circulation through the muscular part of the interventricular septum from right to left. The results suggested that the anatomy, function and embryology of the African monkey, human and porcine heart are not yet fully understood.