Sorcin is a Ca²⁺ binding protein implicated in the regulation of intracellular Ca²⁺ cycling and cardiac excitation-contraction coupling. Structural and human genetic studies suggest that a naturally occurring sequence variant encoding L112-sorcin disrupts an E-F hand Ca²⁺ binding domain and may be responsible for a heritable form of hypertension and hypertrophic heart disease. We generated transgenic mice overexpressing L112-sorcin in the heart and characterized the effects on Ca²⁺ regulation and cardiac function both in vivo and in dissociated cardiomyocytes. Hearts of sorcin^F112L transgenic mice were mildly dilated but ventricular function was preserved and systemic blood pressure was normal. Sorcin^F112L myocytes were smaller than control cells and displayed complex alterations in Ca²⁺ regulation and contractility, including a slowed inactivation of L-type Ca²⁺ current, enhanced Ca²⁺ spark width, duration, and frequency, and increased Na⁺-Ca²⁺ exchange activity. In contrast, mice with cardiac-specific overexpression of wild-type sorcin displayed directionally opposite effects on L-type Ca²⁺ channel function and Ca²⁺ spark behavior. These data further define the role of sorcin in cardiac excitation-contraction coupling and highlight its negative regulation of SR calcium release. Our results also suggest that additional factors may be responsible for the development of cardiac hypertrophy and hypertension in humans expressing the L112-sorcin sequence variant.--Collis, L. P., Meyers, M. B., Zhang, J., Phoon, C. K. L., Sobie, E. A., Coetzee, W. A., Fishman, G. I. Expression of a sorcin missense mutation in the heart modulates excitation-contraction coupling.