We earlier developed the mathematical model of electrical and mechanical activity in myocardium, which takes into account both direct coupling and feedback between excitation and contraction. In this paper, in the framework of the model we found conditions under which both the abrupt shortening and stretch of cardiac preparation can cause extra action potentials and hence anomalous deformations can be arrhythmia sources. In the framework of the model, we establish possible mechanisms underlying the Anrep phenomenon that reflects a relationship between myocardium contraction and vascular resistance in the intact heart.