In anatomy, the<unk> s of the heart serve to limit the movements of the mitral and tricuspid valves. These muscles contract to tighten the chordae tendineae, which in turn prevent inversion. This occurs in response to pressure gradients. Instead they brace the valves against the high pressure, preventing regurgitation of ventricular blood back into the atrial cavities.
Image courtesy of Hartwig, Walter C., The Editor of Fundamental Anatomy, 1st Edition, 2008 and copyrighted 
Image courtesy of Hartwig, Walter C., The Editor of Fundamental Anatomy, 1st Edition, 2008 and copyrighted
Image courtesy of Hartwig, Walter C., The Editor of Fundamental Anatomy, 1st Edition, 2008 and copyrighted
Image courtesy of Hartwig, Walter C., The Editor of Fundamental Anatomy, 1st Edition, 2008 and copyrighted
Papillary muscle
Cardiac muscle
Epicardial fat pad
Endocardium
Ventricle 
Epicardium
External intercostal muscles
Soleus muscle