Cardiac muscle is one of the three types of muscle in mammals. It is myogenic striated muscle that forms the structure of the heart. Cardiac muscle contracts like skeletal muscle; the shortening of the sacromere causes the contraction on the muscle.
The structure of cardiac muscle are long, cylindrical cells with one, sometimes two, nuclei. They branch out into 'Y' shapes. There is a rich blood supply provided by the vast capillary network. This is necessary due to the high level of energy required for the typical heart function. This capillary network is supported by connective tissue between these cardiac muscle fibres. There are also far more mitochondria in cardiac muscle than typical skeletal muscle as the production of ATP is essential to cardiac muscle function, unlike most muscles in the body they are constantly contracting and relaxing thus requiring far more energy than in skeletal muscle. 
Between each cardiac muscle filament, there a intercalated discs found at the junction between cells. These discs are formed of desmosomes and they hold the cells together over the gap junctions.This allows action potentials to move with lower resistance. 
- ↑ Alberts, B. et al 'Molecular Biology of the Cell' Fifth Edition (2008) p.1031, Abingdon, Garland Science, Taylor &amp;amp;amp;amp; Francis Group LLC
- ↑ Lemieux H, Hoppel C. Mitochondria in the human heart. Journal of Bioenergetics and Biomembranes [Internet]. 2009 [cited 3 December 2017];41(2):99-106. Available from: https://www.ncbi.nlm.nih.gov/pubmed/19353253
- ↑ Queen Margaret University (2012) 'Excitable Tissues' [Online] Available at http://www.qmu.ac.uk/hn/appliedscience/D%20Excitable%20Tissues/cardiac_muscle.htm [Accessed on 27/11/2014]