Comparison of the Beats in Three and Four Chambered Hearts

Abstract

A careful observation of the beating hearts of the cat and turtle shows a marked dissimilarity in the manner of contraction. The cat heart appears to remain relatively constant in length, but expands and contracts laterally with each beat, while the turtle heart may be seen to contract uniformly in all directions, as a ball of muscle.

In our attempt to examine this phenomenon in a quantitative way, we used the method outlined by Takeuchi 1 who used cinematographs to examine volume changes of the heart during anoxemia. In our experiments a 16 mm Filmo motion picture camera was used to photograph the beating hearts, exposed in situ, at speeds of either 8 or 16 pictures a second. Light was obtained from Eastman photo-flood lamps.

After the pictures had been taken, each frame was studied under the binocular microscope, using an ocular micrometer which gave a value of one ocular unit equal to 1/2 mm. By means of this, measurements were made of the greatest width and length of the ventricular picture on successive frames for 5 or 6 beats. The amount of change could be plotted graphically against time (in exposures) to form curves similar to the kymograph cardiogram. From these curves the actual dimensions of the hearts during the cycle could be determined for any point on the cycle. Differences between systolic and diastolic sizes along the 2 axes studied were then translated into percentages of the maximum dimensions.

From the above data it may be seen that the ratio between the contraction of the width and length in the heart of the turtle is much nearer 1.0 than is the ratio of the cat's heart. In most cases the turtle ventricle contracts longitudinally even more than it contracts transversely, thus giving ratios of less than 1.0, in distinct contrast to the condition in the cat.