PURPOSE OF REVIEW: We focus on the molecular and cellular basis of the improvement in myocardial energetics, which might represent an attractive therapeutic option in some forms of acute and chronic heart disease. RECENT FINDINGS: Myocardial dysfunction, whether related to left ventricular hypertrophy, heart failure or myocardial ischaemia, is frequently associated with impairment of myocardial energy balance. It is now apparent that this energetic impairment plays a pivotal role, not only in the evolution and outcomes of these disorders but also frequently in their pathogenesis. Despite the fact that energetic impairment may arise for many complex reasons, and the difficulty both in assessing the impairment in vivo and in determining its precise mechanism(s), a number of drugs have become available for treatment of ischaemia and heart failure, as well as potentially for limitation of pathological left ventricular hypertrophy, which act primarily by altering myocardial metabolism so as to improve energetic status. Recent studies with perhexiline and trimetazidine, agents which induce a 'metabolic shift' from long-chain fatty acid to glucose utilization, have demonstrated the utility of this therapeutic principle. SUMMARY: There is ongoing need for more complete mechanistic understanding of the 'metabolic agents', as well as for the large-scale clinical trials of their impact on health outcomes.