Heart failure is a common condition: according to a new study in 11 high-income countries, an estimated 1-2% of the population has heart failure. One feature of late-stage heart failure is nicotine adenine dinucleotide (NAD+), which leaves heart muscle cells unable to generate sufficient ATP to meet their energy needs. Now, investigators at The Hospital for Sick Children and the University of Toronto have shown that this metabolic dysfunction is present early in heart failure, and precedes any sign of clinical dysfunction in the heart.