A biological pacemaker composition for implantation into cardiac tissue includes an effective amount of interstitial cells of Cajal (ICC) to produce or conduct pacing stimuli and thereby modulate cardiac contraction. The biological pacemaker may be included as part of a heart pacing system that includes an implantable electric pacemaker for producing backup pacing stimuli if the at least one biological pacemaker is unable to modulate cardiac contraction at a predetermined pacing rate. Methods for preventing cardiac pacing or conduction dysfunction in a heart include implanting the biological pacemaker or the heart pacing system into the heart.
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