Background: Obesity has been confirmed to be associated with cardiovascular disease, but previous studies have focused on adults, and whether childhood obesity is associated with cardiovascular disease in adulthood needs further research. Objective: This Mendelian randomization (MR) study aimed to investigate the associations of childhood and adult body mass index (BMI) with the risk of chronic heart failure (CHF) and ischemic stroke (IS). Methods: Independent genetic instruments, demonstrating a strong association with exposure at the genome-wide significance level (P