1. The spontaneous contractions of isolated guinea pig atria were arrested by a temperature change in the medium from 30 to 20°C within 20 min.
2. When thiamine tetrahydrofurfuryl disulfide (TTFD) at concentration of 10^-5g/ml was added in the medium, the arrest was not seen for more than 30 min.
3. Arrhythmic contractions induced by the electrical square wave stimulation at threshold intensity were prevented by TTFD at 10^-4g/ml which was added to the medium.
4. These effects of TTFD at respectivee concentrations were seen even 30 min after the drug was removed from the medium, when the atria had been pre-incubated with the drug for one hour before the removal.
5. From these results, it was assumed that TTFD might show these effects against the extrinsic physical invasions through the stabilization of the tissue membrane.