Objective: Ca²⁺ release from the cardiac junctional sarcoplasmic reticulum (SR) is regulated by a complex of proteins, including the ryanodine receptor (RyR), calsequestrin (CSQ), junctin (JCN), and triadin 1 (TRD). Moreover, triadin 1 appears to anchor calsequestrin to the ryanodine receptor. Methods: To determine whether triadin 1 overexpression alters excitation–contraction coupling, we examined the effects of cardiac-specific overexpression of triadin 1 on SR Ca²⁺ handling and contractility in transgenic (TG) compared to wild-type (WT) mice. Results: The overexpression of triadin 1 was associated with an enhanced SR Ca²⁺ load, reflected by a 22% higher amplitude of caffeine-induced Ca²⁺ transients. The decline of Ca²⁺ transients during caffeine exposure was prolonged by 57%. The detection of resting spontaneous SR Ca²⁺ release events (Ca²⁺ sparks) revealed an increased amplitude (by 16%), decline (by 47%), and width (by 47%) in TG. This was associated with a redistribution of Ca²⁺ spark amplitudes from one population to two populations. Measurement of cardiac function by echocardiography and left ventricular (LV) catheterization revealed a decreased cardiac contractility in vivo. The impaired response to β-adrenergic receptor (β-AR) stimulation in TG hearts was associated with an increased protein expression of β-AR kinase 1. In addition, the increase of the L-type Ca²⁺ peak current and the increase of phospholamban (PLB) phosphorylation at Thr¹⁷ were reduced under β-AR stimulation. Conclusion: Taken together, our data suggest that triadin 1 overexpression results in a complex modulation of SR Ca²⁺ handling, which may contribute, at least in part, to the depressed basal contractility and the blunted response to β-adrenergic agonists in TG mice.