We evaluated the effects of halothane and isoflurane on force, action potential, and staircase, an indicator of sarcoplasmic reticulum function, in right ventricular papillary muscles from 4- to 8-day rabbits using a single sucrose gap myograph at a low baseline stimulating frequency of 12 min-1. The ED50 for depression of peak force was 0.25% for halothane and 0.54% for isoflurane. Both anesthetics were more depressant to neonatal myocardium than has been reported in adult myocardium. The ratio of ED50 in neonatal myocardium to that reported in adult myocardium was similar for both anesthetics (0.42 and 0.39). Both anesthetics decreased the height of the plateau phase of the action potential by an equivalent amount but neither affected action potential duration.