Background: Young adulthood is a critical life course window during which cardiovascular pathophysiology develops, yet diet quality and physical activity (PA) are typically studied as separate, static exposures. We examined joint associations of diet and PA across young adulthood with midlife cardiovascular health (CVH) patterns. Methods: Among 2,806 participants in the biracial Coronary Artery Risk Development in Young Adults (CARDIA) cohort, group-based dual-trajectory modeling identified latent classes of joint Dietary Approaches to Stop Hypertension (DASH) score and PA from exam Year 0 to Year 20 (mean age range at each exam 25-45 years). Group-based trajectory modeling defined midlife CVH trajectories using Life's Essential 8 (LE8) scores (5 physiologic components) from Year 20 to Year 35 (mean age range at each exam 45-60 years). Multinomial logistic regression, adjusted for age, sex, race, and education, related young-adult behavioral groups to midlife CVH status (high ?80, moderate 50-79, or low