The STH Pump Controller provides an automatic feedback system for flow and pressure in an isolated heart preparation. When choosing an alternative pump it should only cause small oscillations between pump rollers to prevent the STH making inappropriate adjustments to the system pressure. The pulsatile flow from a peristaltic pump with only a few rollers is enough to trigger the STH to respond within each revolution of a pump head. Pumps with many rollers have smooth flow that allows the STH to respond when the perfusion pressure drops. This is one reason why the Gilson pump is recommended as it has a pump head with 12 rollers, and provides a small flow. Other requirements for an alternative pump are that it's speed can be controlled by an analog voltage output (~0-5V), and it can be started and stopped using a TTL electrical pulse.