We describe our laboratories’ experimental methods for interrogating cardiac energetics – at the organ (whole‐heart), tissue (trabecula) and perforated fibre (mitochondrial) levels. In whole‐heart and trabecula experiments, we focus on measuring pressure‐volume (force‐length) work and oxygen consumption (heat production) from which mechanical efficiency is derived. In both preparations, i.e., across scales differing by three orders of magnitude, we find efficiency values of 10‐15%. Mitochondrial experiments invoke a trio of titration protocols to yield information on oxygen consumption, ATP flux, membrane potential, electron leak and ROS production, the latter two of which index energy transfer inefficiencies. This article is protected by copyright. All rights reserved.