The zebrafish (Danio rerio) is a new animal model
for cardiac research.1–3 Its heart contains four components
(sinus venosus, atrium, ventricle, and bulbus
arteriosus). Although it is equipped with a
prototypic vertebrate heart, the studies of genetic
control for zebrafish development can reveal some
hints to solve human problems.4 In response to
the lack of a transgenic line of zebrafish labeled
with heart-specific fluorescence in vivo to serve as
a research model, we have successfully developed a
cardiac-specific promoter containing the upstream
sequence of the zebrafish cardiac myosin light
chain 2 gene (cmlc2) and generated several germ
lines of transgenic zebrafish that have green fluorescent
protein (GFP)-tagged hearts.5 However, excess
cardiac expression of GFP has been reported to
cause dilated cardiomyopathy in mice.6 Therefore,
we performed this study to evaluate the morphology
and functioning of zebrafish hearts with different
expressional levels of green fluorescence.