The Langendorff Apparatus Unit is a self-contained and thermostatically controlled unit for the perfusion of small animal hearts. It contains two separate perfusate reservoirs that are constantly oxygenated and kept at a constant bath temperature. When used as part of the Langendorff System, the solutions pass through tubes around the Peristaltic Pump (regulated by the STH Pump Controller) in order to pressurize them.