Heart strings (tendons) inside the human heart. (source)  Don't pull on my heartstrings.
{"Image ImageDescription": "Macro photograph of the chordae tendineae in a human heart ventricle (1 of the 2 lower, large muscular chambers of the heart). The chordae tendineae are stringlike processes that attach the outer parts of the mitral & tricuspid valves (dividing the left & right atria and ventricles respectively) to projections in the wall of the ventricle (ie connecting with the capillary muscles). Rupture of the chordae, through injury, endocarditis or degeneration results in mitral incompetence (the failure of the mitral valve leading to a reflux of blood from the lower ventricle to the upper atrium).", "Image Orientation": "Horizontal (normal)", "Image Copyright": "FRIEDER MICHLER/SCIENCE PHOTO LIBRARY", "Image ExifOffset": "694", "EXIF ColorSpace": "Uncalibrated"}