A growing number of studies from a range of different countries have observed an association between sleep duration and cardiovascular disease. The objective of this paper was to examine the associations between sleep duration and prevalent cardiovascular disease in a large sample of Australian adults, and identify the sociodemographic and health-related factors moderating these associations. Participants included 218 155 Australian adults aged 45 years and over. The results indicated that 6 h versus 7 h sleep was associated with increased odds of heart disease [odds ratio (OR) = 1.11 (1.06–1.17)], diabetes [OR = 1.15 (1.09–1.22)], stroke [OR = 1.25 (1.14–1.38)] and high blood pressure [OR = 1.08 (1.04–1.11)]. Long sleep (≥9 h sleep) was also related to elevated odds of heart disease [OR = 1.14 (1.09–1.19)], diabetes [OR = 1.25 (1.19–1.31)], stroke [OR = 1.50 (1.38–1.62)] and high blood pressure [OR = 1.04 (1.01–1.08)] compared to 7 h sleep. Some of these relationships varied by age, and were not evident in adults aged 75 years and over. The magnitude of some associations varied significantly by body mass index, smoking and physical activity. These findings provide further insight into the nature of the relationship between sleep and cardiovascular health.