According to their writings, ancient Greek physicians had explored the anatomy of the heart. Although pre-Hippocratic medicine, which relied on religion and mysticism, has nothing more to present than implausible theories and speculations, younger physicians thanks to their animal dissections were able to depict the heart with detail. Hippocratic "On the Heart", Aristotle's, Herophilus', Erasistratus' and Galen's writings provide us with the necessary data to take a look at the anatomy of the heart as it was described back then. Despite of some confusing passages in their writings and some erroneous notions, the heart was described with relative accuracy. In the years after antiquity and in the Middle Age the only information about the anatomy of the heart could be derived from the ancient Greek works and only anatomists of the Renaissance managed to displace them. In this paper we present the knowledge of all known ancient Greek physicians about the heart, with emphasis on its anatomy.