This initial thought led Harvey's ambition and assiduousness to a detailed analysis of the overall structure of the heart (studied with less hindrances in cold-blooded animals). After this, Harvey goes analyses the arteries, showing how their pulsation depends upon the contraction of the left ventricle, while the contraction of the right ventricle propels its charge of blood into the pulmonary artery. Whilst doing this, the physician reiterates the fact that these two ventricles move together almost simultaneously and not independently as had been thought previously by his predecessors. This discovery was made while observing the heart of such animals as the eel and several other types of fish; indeed, the general study of countless animals was of utmost importance to the physician: among the ones already cited, one can add the study of the snail, the invisible shrimp, the chick before its hatching and even the pigeon. A digression to an experiment can be made to this note: using the inactive heart of a dead pigeon and placing upon it a finger wet with saliva, Harvey was able to witness a transitory and yet incontrovertible pulsation. He had just witnessed the heart's ability to recover from fatigue.