The heart is a hollow, fibromuscular organ in the shape of a distorted cone. It is sited retrosternally between the lungs in the middle mediastinum. It is encapsulated by the layers of the pericardium which form the pericardial cavity. A number of great vessels span the pericardial cavity to the heart. The majority of the organ is on the left side of the thoracic cavity. It slopes obliquely to its apex on the left anteriorly from its posterior base on the right.
The heart has four chambers separated by valves. There is an atria and a ventricle in series on both sides of the heart. The right side is a low pressure circuit for passing venous blood from the body to the lungs. The left side is a high pressure circuit that receives oxygenated blood from the lungs and redistributes it back to the body.
The heart has a complex system of electrical conduction that ensures that the correct sequence of contraction occurs between chambers. The blood supply to the heart is via the coronary arteries which run beneath the epicardium, the most superficial of the three heart layers.
The external surface of the heart can be described in terms of a number of surfaces, borders and grooves or sulci.
Typically, the dimensions of the heart are approximately:
On average, male hearts are heavier than female hearts: 300g compared to 250g.
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