Compartments and suborgans of the ventricular myocardium.

Color-coded liquid plastic was injected intraparenchymally (not into the blood vessels) into more than 300 hearts of homeotherms--including dog, cat, sheep, beef, horse, mammalian dolphins, chickens, turkeys, etc. The organization of the hearts of all these species appears to be similar. After injection of a heart segment such as the right ventricular free wall, corrosion (digestion) of the heart in strong alkali releases the case of only this free wall, and of the lymphatic vessels which drain this segment. None of the injected plastic enters the left ventricular free wall or the septum. Color-coded injections reveal that injections into only the left ventricular free wall, followed by digestion of the heart releases a cast of only the left ventricular free wall. Injection into the septum produces a cast of only the septum. Injection into all three compartments provides a cast of the apex and midpoint of the heart. The colors and injections remain discrete--they never mix. This is evidence that fibrous supercapsules separate these three compartments. The casts prepared by injection into the middle or inferior parts of the ventricular myocardium show large lacunae at the base. Similar injection experiments show that the base of the heart consists of two discrete suborgans: the inflow tract or cushion (tricuspid and mitral rings, and their papillary muscles), and the outflow tract or infundibulum (muscular bundles inferior to the pulmonary and aortic outlets). Further studies showed that the septum consists of discrete right and left hemiseptae. These data support the hypothesis that the heart consists of three suborgans; the cushion, venter (pump), and infundibulum. Each suborgan consists of four compartmetns: its free right wall, free left wall, and right and left hemiseptae. These entirely separate twelve compartments of the ventricular myocardium are held together by strong fibrous connective tissues. Their function is coordinated by the atrioventricular conduction system. The present studies indicate that earlier studies which have indicated that the heart consists of one or two bandage-like, concentric wrappings may be incorrect. The significance of our findings is dicussed.