The aim of this proposal is to enhance cardiac function by genetic engineering, with the long-term goal of halting, reversing or preventing contractile dysfunction in diseased myocardium. The proposal is focused on the calcium binding protein parvalbumin (Parv), and how it directly affects cardiac performance at the cellular, organ and organismal levels. Parv is a small, soluble protein that belongs to the E-F hand family of calcium binding proteins. Parv is naturally expressed in fast-twitch muscle where it facilitates rapid muscular relaxation. Parv is not naturally expressed in the heart. The overarching hypothesis of this application is that over an optimal range of parvalbumin expression in cardiac muscle, both cardiac myocyte relaxation kinetics in vitro, and heart organ diastolic function in vivo will be enhanced while retaining both normal systolic function and beta-adrenergic-mediated cardiac reserve. The Specific Aims are: Aim 1. To define the cellular capabilities and potential limitations of Parv gene transfer/expression in single adult cardiac myocytes. Sub Aim 1 a: To establish the Parv expression threshold and optimal expression range for obtaining improved relaxation function in cardiac myocytes. Sub Aim 1 b: To determine the force-frequency relationship in Parv expressing cardiac myocytes. Sub Aim 1 c: To determine and compare the effects of beta-adrenergic stimulation on the contraction in myocytes after Parv and calcium pump-SERCA-2a gene transfer. Aim 2. To determine the effects of cardiac-directed expression of Parv at the whole organ and organismal levels in transgenic mice. Sub Aim 2a: To generate transgenic mouse lines expressing low, moderate, and high levels of Parv ectopically in the heart. Sub Aim 2b: To establish Parv expression-dependent effects on cardiac hemodynamic function in vivo. Sub Aim 2c: To establish the relationship between Parv expression and performance at differing pacing rates, and in the presence/absence of adrenergic stimulation in the isolated heart. Sub Aim 2d: To establish the long-term effects of Parv expression on in vivo cardiovascular function using radiotelemetry in fully conscious and untethered mice. At moderate Parv expression, the hypothesis to be tested is that systolic heart function will be enhanced; for very high Parv expression (>0.4 mM), systolic cardiovascular function will diminish, and will be exacerbated by exercise. Together, these integrated Specific Aims and hypotheses provide the necessary basic biological foundation on which to fully assess the potential therapeutic capabilities and limitations of Parv expression in the heart.