The heart is a self-renewing biological pump that converts chemical energy into mechanical energy. The entire process of energy conversion is subject to complex regulation at the transcriptional, translational and post-translational levels. Within this system, energy transfer occurs with high efficiency, facilitated by a series of compound-conserved cycles. At the same time, the constituent myocardial proteins themselves are continuously made and degraded in order to adjust to changes in energy demand and changes in the extracellular environment. We recently have identified signals arising from intermediary metabolism that regulate the cycle of myocardial protein turnover. Using a new conceptual framework, we discuss the principle of metabolic cycles and their importance for refueling and for rebuilding the failing heart.