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Cardiac excitation-contraction (E-C) coupling is influenced by (at least) three dynamic systems that couple and feedback to one another (Abstract Figure). Here we review the mechanical effects on cardiomyocytes that include mechano-electro-transduction (commonly referred to as mechano-electric coupling, MEC) and mechano-chemo-transduction (MCT) mechanisms at cell and molecular levels which couple to Ca(2+)-electro and E-C coupling reviewed elsewhere. These feedback loops from muscle contraction and mechano-transduction to the Ca(2+) homeodynamics and to the electrical excitation are essential for understanding the E-C coupling dynamic system and arrhythmogenesis in mechanically loaded hearts. This white paper is comprised of two parts each reflects the key aspects from the 2018 UC Davis symposium: MEC (how mechanical load influences electrical dynamics) and MCT (how mechanical load alters cell signaling and Ca(2+) dynamics). Of course, such separation is artificial since Ca(2+) dynamics profoundly affects ion channels and electrogenic transporters and vice-versa. In time these dynamic systems and their interactions must become fully integrated, and that should be a goal for a comprehensive understanding of how mechanical load influences cell signaling, Ca(2+) homeodynamics and electrical dynamics. In this white paper we will emphasize current understanding, consensus, controversies, and the pressing issues for future investigations. Space constraints make it impossible to cover all relevant articles in the field, so we will focus on the topics discussed in the symposium.