The papillary muscles protrude off the inner lining of the heart (the endocardium); off of these muscles, are the chordae tendineae. The chordae tendineae connect to a valve (tricuspid, mitral) and prevent the valve from opening backwards during ventricular systole.
If the chordae tendineae fail to do their job, the valve will not stay closed during ventricular systole and blood will be regurgitated back into the atria. The most common condition we know this to be is mitral valve prolapse.
-Pass with PASS