Ibn al-Nafis

Ibn al-Nafis sets out pulmonary transit through the lungs

Ibn al-Nafis demolished an invisible structure: the pores Galen said pierced the wall between the heart's ventricles.

The septum is solid

In a separate commentary on the anatomical portions of Avicenna's Canon, conventionally dated to around 1242, Ibn al-Nafis explicitly rejected a passage through the interventricular septum and argued that blood must reach the left ventricle from the right by way of the lungs.

The year is widely repeated in modern medical histories, but no day or month is established. Major manuscript catalogues often date the work only to the thirteenth century, and at least one modern review gives 1232 instead.

The route he proposed

His model sent blood from the right ventricle through the vessel now called the pulmonary artery into the lung, where it was dispersed in lung tissue and mixed with air.

The mixture then passed through the vessel now called the pulmonary vein to the left side of the heart. He also inferred small communications between the pulmonary vessels.

He did not claim to have seen them: his own introductory statement says practical anatomy was unavailable to him and that he relied on earlier anatomists for internal forms.

Transit, not circulation

The result was a major alternative to Galenic and Avicennian heart physiology, but it was a theory of pulmonary transit rather than a modern account of complete closed-loop systemic blood circulation.

He did not describe oxygen, gas exchange, or capillaries as observed structures. The account stayed inside medieval vital-spirit physiology: blood mixed with air in the lungs so that pneuma could be generated in the left ventricle.

No securely dated evidence shows a dramatic public reaction or institutional change in 1242 itself.

Sources

Researched 23 Aug 2026 6 sources not yet audited Traditional date

How this was checked

Researched from the web into a fact sheet and rewritten from that sheet. This article has not yet had an independent model audit. How the pipeline works →

Traditional date. Conventionally dated here; the research places it at ~1242.

What the sources leave uncertain

The year 1242 is conventional and widely repeated in modern medical histories, but no day or month is established. Major manuscript catalogues often date the work only to the thirteenth century, and at least one modern review gives 1232 instead.
Because the event is the composition or completion of a text rather than a witnessed public act, “~1242” is safer than treating it as a securely dated publication.
The strongest recent specialist formulation is “pulmonary transit,” not complete “pulmonary circulation,” because Ibn al-Nafis did not describe the modern closed circulatory system.
Whether he personally performed human or animal dissections is debated. His own introductory statement says practical anatomy was unavailable to him and that he relied on earlier anatomists for internal forms.