Cardiac muscle cells or
cardiomyocytes (also known as
myocardiocytes or
cardiac myocytes) are the muscle cells (
myocytes) that make up the
cardiac muscle. Each myocardial cell contains
myofibrils, which are specialized organelles consisting of long chains of sarcomeres, the fundamental contractile units of muscle cells. Cardiomyocytes show striations similar to those on skeletal muscle cells. Unlike multinucleated skeletal cells, the majority of cardiomyocytes contain only one nucleus, although they may have as many as four. Cardiomyocytes have a high
mitochondrial density, which allows them to produce
adenosine triphosphate (ATP) quickly, making them highly resistant to fatigue.