The origin of the heart beat: a tale of frogs, jellyfish, and turtles.

ONE OF THE MOST remarkable phenomena of nature is the incessant rhythmic action of the heart. Although physicians and philosophers have proposed theories to explain the heart beat for centuries, its mechanism remained elusive until a century ago, when a group of young physiologists working with Michael Foster in England unraveled the mystery through a series of elegant experiments. Critical insight into the origin of the heart beat came from studies performed on jellyfish by George Romanes, one of Foster's pupils. Although this research was not initiated to elucidate the origin of the heart beat, Romanes soon recognized its relevance to the work of his mentor. Through their efforts, and those of Walter Gaskell, another of Foster's pupils, the long debate over the origin of the heart beat was eventually settled. Although it was not universally accepted until the present century, the myogenic theory of the heart heat has a long tradition. Galen, whose views influenced Western medical thought for more than a millennium, discovered in the second century that the excised heart of animals often continued to beat for some time. He asserted, "The power of pulsation has its origin in the heart itself.. . The fact that the heart, removed from the thorax, can be seen to move for a considerable time is a definite indication that it does not need the nerves to perform its own function."'A Although Galen did not discuss the mechanism of the heart's automatic activity , he concluded, "The pulsative faculty of the heart has its source in its own substance."2 He has had a long-standing interest in the literature and history of medicine, the history of cardiology, and the development and implementation of advances in diagnostics and therapeutics. heart beat in his monumental work De motu cordis published in 1628, but he did discuss the subject two decades later. Harvey's view reflected the teachings of Aristotle, which held that the blood within the heart triggered cardiac contraction.3 In his De generatione animalium, published in 165 1, Harvey explained, "The pulse has its origin in the blood.. .. the cardiac auricle from which the pulsation starts, is excited by the blood."4 Harvey's theory of the heart beat was essentially myogenic-nerves played no role in its genesis. The neurogenic theory of the heart beat was elaborated by several 17th century anatomists and physicians who were investigating the role of nerves in controlling muscular activity …