Statins inhibit the biosynthesis of L-mevalonate, a precursor of cholesterol. They improve cardiovascular morbidity and mortality, in part, through regression of atherosclerosis secondary to reduced serum cholesterol. However, a body of research has shown that statins also have direct effects on endothelial cells, vascular smooth muscle cells and cardiac myocytes through cholesterol dependent and independent mechanisms, which may contribute to their efficacy. Cholesterol regulates the expression of proteins like caveolins, structural and regulatory components of caveolae, through sterol regulatory elements in promoter DNA sequences. Caveolae are important signalling platforms [1]. Depletion of cellular mevalonate by statins also attenuates production of isoprenoid intermediates and therefore inhibits prenylation and activation of certain signalling molecules, including the small and heterotrimeric G-proteins. Here we investigate for the first time the impact of in vivo statin treatment on contractile function of the adult ventricle. Adult male Wistar rats were given 40 mg/kg simvastatin or saline daily by oral gavage for 2 weeks. Simvastatin treatment decreased time to half (t0.5) relaxation by 25% in field-stimulated single ventricular myocytes (P<0.001; n=34-48 cells; Student’s t-test), without affecting shortening, [Ca2+]i transient amplitude or t0.5 transient decay. This was accompanied by a 173% increase in phosphorylation of troponin I (TnI) at Ser23/24 in ventricular homogenates (P<0.01; n=6). Levels of endothelial nitric oxide synthase (eNOS) and Akt were 265% and 100% higher, respectively, in ventricular homogenates from statin-treated animals (P<0.01; n=6). Additionally, caveolin 1 (Cav-1) and caveolin 3 (Cav-3) expression were attenuated by 34% and 42%, respectively, with statin treatment (P<0.05; n=6). Despite this, myocardial cholesterol was not significantly different between saline and statin groups (7.8 ± 0.4 vs. 7.6 ± 0.2 μg cholesterol/mg total protein; mean ± S.E.M., n=6). Our results show significant positive lusitropy in cardiomyocytes after in vivo statin administration. This is consistent with the observed increase in TnI phosphorylation. Protein kinases A and G (PKA and PKG) both phosphorylate TnI at Ser23/24: this modification reduces Ca2+ sensitivity of the myofilaments and hastens relaxation. PKG could be more relevant since we also observe an upregulation of Akt and eNOS which, through NO, activates guanylyl cyclase, and produces cGMP. Reduced Cav-1 and Cav-3 might further promote NO production since both interact with and inhibit eNOS. Overall, we show a novel effect of statin treatment which could improve diastolic filling of the heart in situ.