Sinoatrial Node
Martin Flack
Martin Flack
Born20 March 1882
Died16 August 1931 | Age 49

Arthur Keith & Martin Flack 1907

Martin Flack, British physiologist, discovered the bodys' natural pacemaker that is responsible for the initiation of the heartbeat in 1907 with his mentor, Scottish anatomist, Sir Arthur Keith.

Heart beating
Heart beating

On a hot summer day in 1906, Martin Flack, a medical student, was studying microscopic sections of the heart of a mole while Arthur Keith and his wife were bicycling through the beautiful cherry orchards near their cottage in Kent. Upon their return, Flack excitedly showed Keith a wonderful structure he had discovered in the right auricle of the mole, just where the superior vena cava enters that chamber.

The Answer
Sir Arthur Keith 1866–1955
Sir Arthur Keith 1866–1955

Keith quickly realised that this structure closely resembled the atrioventricular node as described by Sunao Tawara earlier that year. Further anatomical studies confirmed the same structure in other hearts, which they named the sino‐auricular node.

The discovery of the sinus node or SA node, the electrical system of the heart, provided an anatomical answer to the baffling mystery:
  • “Why does the heart beat?”

There is a remarkable remnant of primitive fibres persisting at the sino‐auricular junction in all the mammalian hearts examined… in them the dominating rhythm of the heart is believed to normally arise.”
Arthur Keith and Martin Flack


Flack later became demonstrator of physiology at the London Hospital and later a lecturer. He served on the Medical Research Council and became the director of medical research for the Royal Air Force . He was appointed a Commander of the Order of the British Empire in the 1919 New Year Honours .
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