Developmental relationships between the structure, blood supply and metabolic pattern of the vertebrate heart.

In the animal kingdom there exist four types of myocardial blood supply: a) spongious musculature alone, which is supplied from the ventricular cavity; b) an inner spongious layer covered by an outer compact musculature with a vascular supply; c) as b), but with capillaries also present in some trabeculae of spongious musculature; d) compact musculature only, supplied from coronary vessels. The development of the compact layer in different species of cold-blooded animals is more closely related to heart weight than to the phylogenetic position of the animal; the total amount of compact musculature increases with increasing heart weight. These facts give additional support to the hypothesis that the development of compact musculature is necessary for the maintenance of balanced blood pressure conditions in larger hearts. The activities of enzymes connected with aerobic oxidation and glucose phosphorylation are higher in the spongious musculature than in the compact layer. The higher aerobic oxidative capacity of the spongious layer correlates with the higher sensitivity of this musculature to the necrogenic action of isoproterenol.