Confocal microscopy enables us to track myocytes in the embryonic zebrafish heart. The Zeiss LSM 5 Live high speedudconfocal microscope has been used to take optical sections (at 3 µm intervals and 151 frames per second) through audfluorescently labeled zebrafish heart at two developmental stages (26 and 34 hours post fertilization (hpf)). This dataudprovides unique information allowing us to conjecture on the morphology and biomechanics of the developing vertebrateudheart. Nevertheless, the myocytes, whose positions could be determined in a reliable manner, were located sparsely andudmostly in one side of the heart tube. This difficulty was overcome using computational methods, that give longitudinal,udradial and circumferential displacements of the myocytes as well as their contractile behavior. Applied strain analysisudhas shown that in the early embryonic heart tube, only the caudal region (near the in-flow) and another point in theudmiddle of the tube can be active; the rest appears to be mostly passive. This statement is based on the delay betweenudmajor strain and displacement which a material point experiences. Wave-like propagation of all three components of theuddisplacement, especially in the circumferential direction, as well as the almost-periodic changes of the maximum strainudsupport the hypothesis of helical muscle structure embedded in the tube. Changes of geometry in the embryonic heartudafter several hours are used to verify speculations about the structure based on the earlier images and aforementionedudmethods.
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