Cardiac action potential to fail, then the heart could continue to beat, albeit at a lower rate (AVN= 40-60 beats per minute, purkinje fibres = 20-40 beats per minute). These pacemakers will keep a patient alive until the emergency team arrives. An example of premature ventricular contraction, is the classic athletic heart syndrome. Sustained training of athletes causes a cardiac adaptation where the resting SAN rate is lower (sometimes around 40 beats per minute). This can lead to atrioventricular block, where the signal from the SAN is impaired in its path to the ventricles. This leads to uncoordinated contractions between the atria and
Cardiac excitation-contraction coupling body is at rest. This rate can be altered, however, by nerves that work to either increase heart rate (sympathetic nerves) or decrease it (parasympathetic nerves), as the body's oxygen demands change. Ultimately, muscle contraction revolves around a charged atom (ion), calcium (Ca), which is responsible for converting the electrical energy of the action potential into mechanical energy (contraction) of the muscle. This is achieved in a region of the muscle cell, called the transverse-tubule during a process known as calcium induced calcium release. Located in the wall of the right atrium is a group of specialised cells, called the