Mice homozygous for this Arrb1 (arrestin, beta 1) targeted mutation produce a cardiac ejection fraction that is greater than that of wildtype mice in response to isoproterenol, a _-receptor agonist. They are viable and fertile and do not display any gross physical or behavioral abnormalities. Life expectancy, fertility, blood chemistry, mean resting blood pressure, resting heart rate and immune systems are indistinguishable from those of wildtype mice. This targeted mutation strain lacks protein expression as determined by Western blot. This strain may be useful for further studies of gene function. The Jackson Laboratory 2024, used with permission.