TNNI3 and cardiomyopathy, familial restrictive, 1: Tβ4 −/Y mice share some features of the murine R193H cTnI mutation model of restrictive cardiomyopathy (RCM) [49]; namely, short ED sarcomere length, regionalized increases in fractional wall thickening, reduced EDV, an inability to increase cardiac output in response to β-adrenergic stimulation or to reduce stroke volume in response to β-blockade.