[The effect of difluorodichloromethane (FC 12) on isolated rat and rabbit heart]

We have tried to determine if dichlorodifluoromethane (F.C. 12) might have an effect in vitro on the isolated rat and rabbit hearts. The direct action of F.C. 12 on the heart in vitro is similar in both rats and rabbits. It occurs at doses such as 20 +/- 10 mug/ml (rat) and 35 +/- 5 mug/ml (rabbit). F.C. 12 depresses the strength of the myocardial contractions; the effect is reversible at low concentration (less than 60 mug/ml) but irreversible at high concentration (greater than or equal to 120 mug/ml). It also causes a slight bradycardia, but no significant effect on the basal tonus. At high concentration, F.C. 12 may produce arrhythmia : this action occurs more readily in the rat heart than in the rabbit heart.