The type 1 protein phosphatase (PP1) is a critical negative regulator of Ca(2+) 
cycling and contractility in the cardiomyocyte. In particular, it mediates 
restoration of cardiac function to basal levels, after beta-adrenergic 
stimulation, by dephosphorylating key phospho-proteins. PP1 is a holoenzyme 
comprised of its catalytic and auxiliary subunits. These regulatory proteins 
dictate PP1's subcellular localization, substrate specificity and activity. 
Amongst them, inhibitor-1 is of particular importance since it has been 
implicated as an integrator of multiple neurohormonal pathways, which finely 
regulate PP1 activity, at the level of the sarcoplasmic reticulum (SR). In fact, 
perturbations in the regulation of PP1 by inhibitor-1 have been implicated in 
the pathogenesis of heart failure, suggesting that inhibitor-1-based therapeutic 
interventions may ameliorate cardiac dysfunction and remodeling in the failing 
heart. This review will discuss the current views on the role of inhibitor-1 in 
cardiac physiology, its possible contribution to cardiac disease and its 
potential as a novel therapeutic strategy.