The protective effect of calcium entry blockers can be studied advantageously on the model of the calcium paradox, particularly on the basis of the preservation of haemodynamic and biochemical parameters as well as on the structure of the myocardium (Meno et al. 1984). Our aim in this study was to test the protective effect of the recently developed Czechoslovak drug diltiazem (LACHEMA) under conditions of the Ca2+ paradox.