What is Cardiac muscle?
{{Infobox anatomy | Name = Cardiac muscle | Latin = Textus muscularis striatus cardiacus | Image = Glanzstreifen.jpg | Caption = Cardiac muscle | Image2 = 414c Cardiacmuscle.jpg | Caption2 = Cardiac muscle tissue is only found in the heart | part_of = [[Myocardium]] of the [[heart]] | System = }} [[File:A single cardiomyocyte beating, five days after purification from cell culture.ogv|thumb|An isolated cardiac muscle cell, beating]] A '''cardiac muscle''' ('''heart muscle''') is one of the three main types of muscle in [[vertebrates]]. It is involuntary: a person cannot control it [[consciousness|consciously]]. Also, it is a [[:en:Striated_muscle_tissue|striped muscle]] in the walls of the [[heart]]. It makes up the [[tissue]] called the '''myocardium'''. The other types of muscle are the [[skeletal muscle|skeletal]] and [[smooth muscle]]. The cells that make up cardiac muscle have one (74%) or two (24.5%) [[cell nucleus|nuclei]].<ref>{{cite journal |author=Olivetti G; Cigola E & Maestri R. |title=Aging, cardiac hypertrophy and ischemic cardiomyopathy do not affect the proportion of mononucleated and multinucleated myocytes in the human heart |journal=Journal of Molecular and Cellular Cardiology |volume=28 |issue=7 |pages=1463–77 |date=July 1996 |pmid=8841934 |doi=10.1006/jmcc.1996.0137 |url=http://www.sciencedirect.com/science/article/pii/S0022282896901376|display-authors=etal}}</ref><ref>Pollard, Thomas D. and Earnshaw, William. C. 2007. ''Cell biology''. Philadelphia: Saunders.</ref> The myocardium forms a thick middle layer between the outer [[epicardium]] layer and the inner [[endocardium]] layer. Coordinated [[contraction]]s of cardiac muscle cells in the heart force [[blood]] out of the [[atrium (heart)|atria]] and [[ventricle (heart)|ventricles]] to the blood vessels of the left/body/systemic and right/lungs/pulmonary [[circulatory system]]s. This mechanism illustrates [[Systole (medicine)|systole]] (contraction) of the heart. Cardiac muscle cells, unlike most