The heart is the organ responsible for pumping blood throughout the body and into the lungs.
The heart consists of four chambers - two atria and two ventricles - surrounded by the pericardium, which forms a lubricated, bilayered sac. The heart is divided into left and right sides, each of which contain an atrium and a ventricle. The left side is concerned with pumping oxygenated blood through the body and is typically more muscular; the right receives deoxygenated blood from the body and pumps it to the lungs.
The left atrium is typically posterior, the left ventricle to the left lateral side, the right ventricle anteriorly and the right atrium to the right lateral side.
The heart is related laterally to each of the lungs. The sternum is anterior; the oesophagus and descending aorta are posterior. The superior mediastinum and its contents lie superiorly. The diaphragm divides the heart from the abdominal contents; the left lobe of the liver is typically in relation to the heart beyond this.
Arteries of the Heart
The arteries of the heart are particularly important in radiotherapy, as evidence suggests that there is an increased rate of coronary vascular disease many years after radiation treatment in the vicinity. The heart is supplied by two coronary vessels which arise near the origin of the ascending aorta.
Left Coronary Artery
The left coronary artery initially passes to the left and then curves anteriorly. It divides into the left circumflex (which passes posteriorly between the left atrium and left ventricle) and the left anterior descending artery, which passes anteriorly and inferiorly along the anterior aspect of the interventricular septum. This artery may be involved in tangential breast radiotherapy.
Right Coronary Artery
The right coronary artery is usually smaller than the left, and passes to the right of the pulmonary trunk. It supplies the sinoatrial node (the cardiac pacemaker) and continues along the junction of the right atrium and ventricle. It gives off a marginal branch which passes inferiorly along the right ventricle towards the apex of the heart. The right coronary may communicate with the left circumflex, and one of these two arteries gives rise to the posterior descending artery which mimics the anterior descending, passing inferolaterally along the posterior aspect of the interventricular septum.