Figure 1.

A basic schematic diagram of human left ventricular muscle structure and cardiac muscle-derived microRNAs. A – A sarcomere is composed of myofibrils, each containing myofilaments: the thick filaments are composed of myosin, while the thin filaments are composed of actin, tropomyosin, troponin C, and troponin I. Myosin contains two heads having ATPase activity. Calcium ions (Ca2+) bind via troponin C. miR-208b and miR-499 regulate genes for myosin heavy chains. B – Cardiac muscle cells are striated, branched, involuntary, and usually contain a single nucleus. C – Fibroblasts provide support to cardiac muscle cells, as they are responsible for deposition of extracellular matrix in the heart