As androgen deprivation therapy (ADT) is increasingly being used in men with localised prostate cancer, our goal was to examine the association between ADT and the risk of cardiovascular disease (CVD). We conducted a prospective cohort study using records of a large health-care system in California. The study included men with newly diagnosed localised prostate cancer (1998-2008) who initially underwent active surveillance (N=7637) and were followed through 2010. We examined 10 individual CVD outcomes. Cox proportional hazard models incorporated time-varying treatment variables and controlled for race/ethnicity, age, and tumour characteristics, recurrence risk, CVD medication use, and CVD risk factors. Of the 7637 subjects, nearly 30% were exposed to ADT. In the multivariable analyses, ADT was associated with an increased risk of heart failure (adjusted HR=1.81, 95% CI 1.40-2.32) in men without preexisting CVD. Elevated risks of arrhythmia (adjusted HR=1.44, 95% CI 1.02-2.01), and conduction disorder (adjusted HR=3.11, 95% CI 1.22, 7.91) were only observed among patients with preexisting CVD. In men with clinically localised prostate cancer who were initially under active surveillance, ADT was associated with a greater risk of heart failure in men without any preexisting CVD. We also found an increased risk of arrhythmia and conduction disorder in men with preexisting CVD. This study provides the basis for identifying high-risk men treated with ADT who might benefit from regular cardiac monitoring and lifestyle modification recommendations.