In 1242, the physician Ibn al-Nafis published a groundbreaking commentary on the anatomy of the heart, which fundamentally challenged the long-standing medical doctrines established by Galen. By meticulously dissecting and observing the structure of the heart and lungs, he identified that blood does not pass directly between the ventricles through invisible pores, as previously theorised. Instead, he proposed that blood must travel from the right ventricle to the lungs, where it is refined by air before returning to the left ventricle to be distributed throughout the body.

This description of pulmonary circulation marked a significant departure from the prevailing physiological models of the medieval period. By correctly identifying the movement of blood through the pulmonary artery and veins, Ibn al-Nafis provided a more accurate understanding of the cardiovascular system. His work represents a critical shift in medical history, prioritising empirical observation over the unquestioned acceptance of classical anatomical texts.

The legacy of this discovery remains a subject of historical interest due to the complex nature of its transmission. While his account stands as one of the most sophisticated physiological contributions of the medieval era, its influence on later medical developments was not immediate or linear. Key aspects of his contribution include:

• The rejection of the Galenic theory regarding interventricular pores.
• The identification of the pulmonary artery as the vessel carrying blood to the lungs.
• The recognition of the role of air in the refinement of blood within the lungs.
• The assertion that blood returns to the heart via the pulmonary veins.

The work of Ibn al-Nafis serves as a testament to the rigorous intellectual climate of the time, demonstrating an advanced approach to anatomical study. Although his findings were not universally adopted in the centuries that followed, they remain a vital milestone in the history of medicine, illustrating the early development of modern physiological thought.