The ex vivo isolated heart perfusion model by Oskar Langendorff to resuscitate and maintain the automacity of a heart excised from a mammal was introduced in the late nineteenth century. It has remained an essential technique used for functional studies in cardiovascular research even after over a hundred years. This model provides information on contractility, cardiac rhythm, metabolism, and overall cardiac function. It allows the study of the heart in isolation without the influences of other organs or hormones. It enables the investigation of physiological mechanisms underlying heart function under different conditions with more experimental control than the heart in vivo. This chapter provides an overview of the protocol for the isolated heart perfusion model.