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Sixty-two chick embryo hearts were studied at incremental stages of development (Hamburger-Hamilton stages 16 to 39) by scanning electron microscopy following 3% glutaraldehyde fixation and critical point drying. Early in cardiac development, the primitive ventricle becomes homogeneously trabeculated with highly organized sheets of myocytes lined by endocardial cells, with the trabeculae generally oriented in the dorsoventral direction. Coalescence of these trabecular sheets begins at stage 26, initially at the area of the bulboventricular flange, and later proceeding caudally toward the floor of the ventricle. The fusion process is finished by stage 30, resulting in a muscular ventricular septum that has now divided the primitive ventricle into right and left ventricles. Further growth of the ventricular septum is by continued fusion of the adjoining trabecular sheets. Remnants of the apposing trabecular sheets are found in the solidified muscular septum in the form of endocardial channels. We suggest that persistent patency of these channels results in muscular ventricular septal defects.

M mode echocardiograms were obtained from 654 healthy subjects, 7 to 22 years of age, whose diastolic blood pressure levels remained in the same height-, race-, and sex-specific decile during two biannual examinations. Echocardiographic measures of heart size, obtained according to the recommendations of the American Society for Echocardiography, were compared across the entire systolic and diastolic blood pressure distributions. Echocardiographic indexes of left heart size varied as a function of both blood pressure levels and body size. Significant positive correlations were present between systolic blood pressure and different measures of left ventricular size. Left ventricular wall thickness in systole correlated with systolic blood pressure (r = .42, p less than .0001), and persistence of this relationship was noted after adjustment for body size. Left ventricular wall thickness in diastole correlated with blood pressure before adjustment (r = .31, p less than .0001), but the relationship was not significant after adjustment for body size. The ratio of left ventricular thickness to chamber size (systole) correlated with systolic blood pressure levels both before and after adjustment for body size (r = .20 and r = .22, p less than .001). Male subjects of both races demonstrated significantly higher adjusted left ventricular mass, left ventricular wall thickness, and left ventricular chamber size. Adjusted left ventricular wall stress was significantly related to both systolic (r = .14) and diastolic blood pressure levels (r = .14, p less than .001). Measures of left ventricular wall thickness increased throughout the entire blood pressure distribution, indicating a consistent trend rather than a threshold effect seen only in the highest blood pressure groups.(ABSTRACT TRUNCATED AT 250 WORDS)

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