The heart is a double pump, composed of a special type of muscle, which works continuously, day and night, and even when we are unconscious, from well before birth until the moment of death. The heart is found in all vertebrates and is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions. The term cardiac (as in cardiology) means "related to the heart" and comes from the Greek kardia, for "heart."

The average human heart, beating at 72 beats per minute, will beat approximately 2.5 billion times during an average 66 year lifespan. It weighs on average 250 g to 300 g in females and 300 g to 350 g in males.

The heart is enclosed in a double-walled sac called the pericardium. The superficial part of this sac is called the fibrous pericardium. This sac protects the heart, anchors its surrounding structures, and prevents overfilling of the heart with blood. It is located anterior to the vertebral column and posterior to the sternum. The size of the heart is about the size of a fist and has a mass of between 250 grams and 350 grams.

The heart is composed of three layers, all of which are rich with blood vessels. The superficial layer, called the visceral layer, the middle layer, called the myocardium, and the third layer which is called the endocardium. The heart has four chambers, two superior atria and two inferior ventricles. The atria are the receiving chambers and the ventricles are the discharging chambers. The pathway of blood through the heart consists of a pulmonary circuit and a systemic circuit. Blood flows through the heart in one direction, from the atrias to the ventricles, and out if the great arteries, or the aorta for example. This is done by four valves which are the tricuspid atrioventicular valve, the mitral atrioventicular valve, the aortic semilunar valve, and the pulmonary semilunar valve.

The right hand side of the heart pumps blood to the lungs, where it collects oxygen, vital to all our body processes, and is cleansed of carbon dioxide and other wastes. The left side of the heart pumps the freshly oxygenated blood round the entire body, taking oxygen and other necessary elements to all the organs and tissues.

A few essential oils act on the heart. Borneol, Garlic, Lavender, Marjoram, Peppermint, Rose and Rosemary are all described as cardiac tonics, i.e. they have a strengthening effect on the actual muscle of the heart. Lavender, Melissa, Neroli and Ylang Ylang are recommended for palpitations, and so on, but all of these uses should be approached with great caution, and you should not attempt to treat any heart condition without a medical training; although the oils mentioned can certainly be used in baths and massages for anybody who is already receiving treatment from a qualified practitioner.

Many of the conditions which we generally refer to as 'heart disease' are, in fact, diseases of the circulatory system, most often due to fatty degeneration of the arteries serving the heart itself. If these become constricted or blocked by fatty deposits inside their walls, the heart muscle is starved of oxygen, and as no muscle can function for more than a few moments without oxygen, it stops working. This is what we describe as a 'heart attack' or 'coronary'.

Fortunately, there are a number of essential oils which do have a helpful action on circulatory problems and these are described under the entry for CIRCULATION.