João Rodrigues de Castelo Branco, better known as Amato Lusitano and Amatus Lusitanus (Castelo Branco, 1511 – Thessaloniki, 1568), was a notable Portuguese Jewish physician of the 16th century. Like Herophilus, Galen, Ibn al-Nafis, Michael Servetus, Realdo Colombo and William Harvey, he is credited as making a discovery in the circulation of the blood. He is said to have discovered the function of the valves in the circulation of the blood.
Lusitano was born in Castelo Branco in 1511, of Jewish parents. He studied medicine at the University of Salamanca, Spain. Unable to return to Portugal as he wished, due to the persecutions of the Inquisition, he travelled throughout Europe before settling in Ferrara, Italy, at whose University he taught anatomy as an assistant to the physician Giambattista Canano. He wrote several books, including Index Dioscoridis (1536), In Dioscorides de Medica materia Librum quinque enarrationis (1556), and Curationium Centuriae Septem (1556). He was for a time the physician to the Pope Julius III, in Rome. With the accession of Pope Paul IV, persecutions of the Jews in Italy began. Lusitano fled first to Ragusa, then to Thessaloniki, Greece, which then had a large Jewish community and was part of the Ottoman Empire.