Objective: To review and quantify the dose-response relationship of physical activity (PA) in initially healthy women on cardiovascular disease (CVD) outcomes, especially coronary heart disease (CHD) and stroke, and to assess the minimum amount of PA to reduce CVD risk. Data Sources: Studies on PA and CVD were searched in MEDLINE (January 1966-March 2003) with additional manual searches. Data Selection: Studies were included if they (1) provided data on women; (2) assessed PA (exposure) as either a continuous variable or a categorical variable with three or more levels, and CVD (outcome); and (3) provided information on relative risks (RRs) and 95% confidence intervals. Data Extraction: Studies were reviewed, abstracted, and rated for quality by each author. Data Synthesis: Thirty articles met the inclusion criteria. When studies were combined according to relative PA levels, the RRs showed a dose-response relationship for CHD (RR = 1 [reference], 0.78, 0.53, 0.61, respectively; p for trend was <0.0001 for studies with four PA levels, n = 5); for stroke (RR = 1 [reference], 0.73, 0.68, p for trend was <0.0001 for studies with three PA levels, n = 7); and for overall CVD (RR = 1 [reference], 0.82, 0.78, p for trend was <0.0001 for studies with three PA levels, n = 6). When studies were combined by absolute walking amount, even 1 hour/week walk was associated with reduced risk of CVD outcome. Conclusions: Physical activity was associated with reduced risk of CVD among women in a dose-response fashion. Inactive women would benefit by even slightly increasing their PA (e.g., walking 1 hour per week or possibly less) and even more from additional PA.