Heart Myths and the Real Science

The heart is the organ we feel most directly: we hear it, feel it thump after running and see it drawn on cards and emojis. That familiarity makes it easy to pick up ideas that sound right but are not. Simplified diagrams add to the confusion, because they use colours and shapes that are conventions rather than reality. The myths on this infographic are some of the most common.

Many people put a hand on the left of their chest to point to their heart. In fact the heart sits near the middle of the chest, between the lungs and behind the breastbone. It is tilted so that its lower tip, the apex, points down and to the left. That is where the beat is strongest, which is why the 'left side' idea is so persistent.

A real heart does not look like the symbol on a greetings card either. Anatomists compare its shape to a pinecone: broad at the top, where the large blood vessels attach, and narrowing to a rounded tip. It is roughly the size of a fist.

Blood is always red. Haemoglobin, the protein that carries oxygen in red blood cells, makes oxygen-rich blood bright red and oxygen-poor blood a darker red, but never blue.

Veins look bluish through the skin because of the way light travels through skin and back to your eye: the skin scatters away much of the red light before it can reflect off the blood, so more of the blue light comes back. Diagrams colour oxygen-poor blood blue only so that you can tell the two streams apart.

Your heart does not stop when you sneeze. A sneeze briefly raises the pressure in your chest and affects a nerve that helps to set your heart rate, so the rhythm can change for a moment. Heart monitors that record every beat do not show the kind of pause that would count as the heart stopping.

The familiar 'lub-dub' is not the sound of muscle squeezing. The 'lub' is the tricuspid and mitral valves snapping shut as the ventricles start to contract. The 'dub' is the aortic and pulmonary valves closing as the ventricles relax.

Your brain does not have to order each beat, either. The heart has its own pacemaker, the sinoatrial (SA) node, which fires by itself. Left completely alone, it would set a rhythm of roughly 80 to 100 beats a minute. Nerves from the brain, and hormones, only speed the heart up or slow it down.

The heart moves blood, but it does not make it. Red blood cells, white blood cells and platelets are produced in the red bone marrow inside bones such as the hip bones, breastbone and spine.

It is also tempting to think that the bigger, stronger left ventricle pumps more blood than the right. It does not: both ventricles push out the same amount with each beat, otherwise blood would pile up in one circuit. The left ventricle is thicker because it has to create much higher pressure to send blood all round the body, while the right ventricle only pumps to the nearby lungs.