Cardiac muscle tissues have the extraordinary job to continuously function (nonstop). They strongly rely on ATP for energy, and it needs a constant supply of energy and oxygen to not fatigue out. The muscle is saturated with mitochondria and it has a very complex network of capillaries. However, in order to satiate the energy needed, the heart uses oxidative metabolism, derived from lipids, to produce large quantities of ATP with smaller intensity.
The muscle uses a conduction system to manage and efficiently pump blood, basically a communication system to signal the atria and ventricles to contract. The SA (Sinoatrial) node is a small mass of fibers that controls the heartbeat, while the AV (Atrioventricular) node is a small mass of fibers that conducts electrical impulses from the SA node to the ventricle. Both nodes branch to the left and right chambers of the heart, and are known as bundle branches. The way the nodes communicate with the heart and one another is very interesting. It is known as the wave of depolarization; the first contractile signal originates in the SA node, which gives it its nickname of the pacemaker. It then sends slow signals to the right and left atrium, while it sends a fast signal to the AV node through preferential pathways, where the AV node then sends signals to the ventricles. When the action potential signals transfer to the left and right bundles (bundle branches), this stimulates the contraction of the ventricles.
But what does this all mean? It helps us understand our Cardiac Output and that allows us to determine how much our heat can sustain physical activity. Cardiac Output is the product of our Heart Rate and Stroke Volume. As the heart pumps blood from the ventricle, stroke volume (the blood expelled per contraction) depends on the strength of the contraction. The rate the blood is pumped determines how much blood goes to the tissue. The heart rate is what describes the beats of the heart (typically done in a minute).