Time course and duration of the depressant effect of active shortening in cradiac muscle

Shortening deactivation is studied in isolated preparations of rat cardiac muscle by comparing tension redevelopment in partially fused isometric contractions with quick releases of different extent (“control” and “test” displacements). The active shortening takes place during the ascending phase of the 1^st contraction of the couple and the comparison of redeveloped tension is carried out at the peaks of both 1^st and 2^nd contractions. The depressant effect of active shortening can be demonstrated at the 1^st peak and also at the 2^nd one, after the restimulation of the muscle.