Leonardo's anatomical studies of the heart demonstrate the dependency of form and function on one another and that their combined activity leads to a comprehensive understanding of the cardiovascular system. While Leonardo was able to make incredible deductions regarding the heart's anatomy and physiology through the concepts of form and function, it is evident that his preconceptions hindered him from realizing the full scope of his individual findings. In this paper, I will evaluate the perception of anatomy, the manner in which anatomical knowledge was acquired, and the resultant traditional understanding of the cardiovascular system during Leonardo's lifetime. Leonardo's drawings of the heart will then be analyzed to determine what conclusions he was able to make regarding the heart's anatomy and physiology. Finally, I will compare Leonardo's findings to the modern understanding of the cardiovascular system. Because Leonardo's anatomical studies were hidden from the world for so long, many of his conclusions regarding the heart did not come to light before other individuals had already begun to reach them on their own. Although he made incredible leaps in the understanding of the cardiovascular system, he made little contribution to modern cardiology. Now Leonardo's work can only be examined retrospectively to determine the accuracies and inaccuracies of Leonardo's conclusions in comparison to our modern understanding.