An infrared heat source for temperature control of a small microscope flow bath

A simple, inexpensive, and easily installed infrared heat source with temperature controller for small superfusion baths used in electrophysiologic experiments is described. The output of a thermal sensor in the bath is amplified and sent to a feedback circuit which in turn controls the voltage supplied to a tungsten/halogen bulb focused on the bath. Fluctuation from the set point is no more than 0.2 degrees C with good fluid level control. Judging from the lack of change in the cardiac action potential duration, heart cells do not preferentially absorb infrared radiation.