In an experimental study to investigate the effect of constant light on longevity in heart disease male hamsters with inherited heart disease were housed in pairs in either constant light or 12 h light and 12 h dark cycles. All hamsters had free access to food and water. Constant light slowed the progress of heart failure, made the hamsters more likely to survive the early stages of failure, and extended their lives. This observation may open new avenues for the treatment of human beings with heart disease.