The coronary arteries provide the main blood supply to the heart. The coronary arteries also supply the myocardium with oxygen to allow for the contraction of the heart and thus causing circulation of the blood throughout the body. Two main coronary arteries originate from the base of the aorta as it exits the left ventricle: the left and right coronary arteries. These arteries further branch into smaller arteries to supply specific parts of the heart like the atria, ventricles, SA and AV nodes. It is important to realize that the paths these arteries take may vary slightly from person to person.
The function of the arteries of the heart is to provide oxygen and nutrients to the myocardium to allow for contraction of the heart which causes blood to circulate throughout the body. The arteries of the heart are also capable of autoregulation and can control the amount of blood flow being supplied to the heart according to its need. The coronary arteries receive the most blood flow during diastole because this is when the heart is relaxed, and they received the least blood flow during systole because this is when the myocardium contracts are decreasing the blood flow through the coronary arteries.
The coronary arteries split into two, main arterial branches from the base of the aorta. They are the left and right coronary arteries:
The left coronary artery (LCA) extends along the coronary sulcus and supplies the left portion of the heart. It further branches into the circumflex artery and the anterior interventricular artery (left anterior descending artery). The anterior interventricular artery further divides into septal branches and diagonal branches.
The right coronary artery (RCA) traces along the right coronary sulcus and provides blood flow to the anterior and diaphragmatic surfaces of right atrium and ventricle; as well as the posterior two-thirds of the interventricular septum.
Anastomosis occurs in a few places of the heart even though the coronary arteries are considered end arteries.
Coronary Venous Anatomy
Just like the coronary arteries, there are coronary veins which drain the myocardium of deoxygenated blood. In general, there is twice the number of coronary veins as arteries, and the flow occurs during both systole and diastole.
The coronary veins are organized into two groups: greater and smaller cardiac veins. The greater cardiac veins consist of the coronary sinus, atrial veins, anterior cardiac veins and veins draining the septum. The greater cardiac veins account for 95% of all venous drainage from the heart. The smaller cardiac veins also known as the thebesian veins are luminal vessels and drain directly into the respective cardiac chambers.
All the venous blood from the heart arrives at the coronary sinus which is located in the atrioventricular groove. The coronary sinus is the biggest cardiac vein, and it empties directly into the right atrium at the conjunction of the coronary and the interventricular grooves. The coronary sinus does have a small valve-like structure.
The medulla provides sympathetic and parasympathetic innervation to the heart and coronary arteries. The sympathetic innervation is via the cardiac fibers from the superior, middle and inferior cervical ganglion. Sympathetic innervation causes vasodilation of the coronary arteries. The parasympathetic innervation is via the vagus nerve. The vagus nerve will constrict the coronary arteries.
There are many anatomic variations in the blood supply of the heart. One of the biggest distinctions is determining whether the heart is RCA dominant, LCA dominant or codominant. The dominance of the heart depends on where the PDA is derived from.
Important congenital coronary artery anomalies exist. Children born with an anomalous left coronary from the pulmonary artery (ALCAPA) present with congestive heart failure around 4-6 months of age. An anomalous left coronary artery from the right sinus coursing between the pulmonary artery and the aorta is associated with sudden death during exercise. 
Coronary artery disease is uncommon in young people except in rare cases of homozygous familial hypercholesterolemia. 
Percutaneous coronary intervention (PCI) are non-surgical procedures that are recommended once a patient is diagnosed with unstable angina, non-ST elevated myocardial infarction or ST-elevated myocardial infarction. PCI includes procedures such as angiography, angioplasty and stent placement and should be done within 90 minutes of the patient's arrival to the emergency room. These procedures are done in the cath lab help visualize the obstruction and revascularize the heart. Angioplasty allows the visualization of the arteries and localizing of the narrowing of the coronary artery. After narrowing is identified a balloon angioplasty can be done where a balloon is inflated causing expansion of the narrowed artery and improving blood flow. A stent is a mesh tube that can be placed to keep the coronary artery open.
A myocardial infarction occurs when there is a narrowing or occlusion of a coronary artery due to atherosclerosis (plaque buildup due to cholesterol). In an infarction blood supply is insufficient to the contracting myocardium and oxygen supply does not meet oxygen demand causing cell death. This causes an ST segment elevation on an ECG due to abnormal conduction through the heart.
Coronary arteries are end arteries, and this means there is only one source of blood supply to the myocardium increasing the risk of endocardial damage due to narrowing.
Considering that the function of the arteries is to supply the heart with oxygen, it is important to know which artery supplies which portion of them in order to be able to read an electrocardiogram (EKG). Knowing which leads in an ECG correspond to specific arteries help localize the location of the obstruction which can product predictable patterns. 
Anomalous coronary arteries can be a diagnostic challenge. They may occur either singly or in combination with other congenital heart disorders. The incidence of anomalous coronary vessels has been reported to be about 0.1% to 0.3% in necropsy reports. Although rare, they can often present with hemodynamic abnormalities. Many coronary anomalies are first identified on an angiogram because of their anomalous course.
Type of coronary anomalies
High Takeoff: where the origin of the LCA or RCA is above the usual anatomical location. These anomalies may present with difficulty in cannulation during angiography.
Multiple ostia where the RCA and the conus branch may arise separately, or the LAD and left circumflex may arise with no left common coronary artery.
Single Coronary Artery: when there is only one coronary artery arising from the aortic trunk. It may be the RCA or the LAD. If the single coronary passes between the aorta and pulmonary artery, it can be compressed and present with sudden death.
Anomalous origin of the coronary artery from the pulmonary artery is the most serious congenital coronary artery anomaly. Most infants are symptomatic at birth. In the most common type, the left common coronary arises from the pulmonary artery with the RCA arising normally. These patents need some procedure to convert it into a dual coronary artery system. The bypass can be conducted with saphenous vein graft or internal mammary, but the small size of the coronary is a major limiting factor. Rarely, this can present in adolescents an adults. 
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