Chronic diabetes is often associated with cardiomyopathy, which may result, in part, from defects in cardiac muscle proteins. We investigated whether a 20-week porcine model of diabetic dyslipidemia (DD) would impair in vivo myocardial function and yield alterations in cardiac myofibrillar proteins and whether endurance exercise training would improve these changes. Myocardial function was depressed in anesthetized DD pigs (n=12) compared to sedentary controls (C, n=13) as evidenced by an ~ 45% decrease in left ventricular fractional shortening and 35% decrease in +dP/dt measured by non-invasive echocardiography and direct cardiac catheterization, respectively. This depression in myocardial function was improved with chronic exercise as treadmill-trained DD pigs (DDX) (n=15) had significantly greater fractional shortening and +dP/dt than DD animals. Interestingly, the isoform expression pattern of the myofibrillar regulatory protein, cardiac troponin T (cTnT), was significantly shifted from cTnT₁ toward cTnT₂ and cTnT₃ in DD pigs. Furthermore, this change in cTnT isoform expression pattern was prevented in DDX pigs. Finally, there was a decrease in baseline levels of cAMP-dependent protein kinase-induced phosphorylation of the myofibrillar proteins troponin I (cTnI) and myosin-binding protein-C (MyBP-C) in DD animals. Overall, these results indicate that 20 weeks of diabetic dyslipidemia leads to myocardial dysfunction coincident with significant alterations in myofibrillar proteins, both of which are entirely prevented with endurance exercise training, implying that changes in myofibrillar proteins may contribute, at least in part, to cardiac dysfunction associated with diabetic cardiomyopathy.