Background. Cardiovascular disease (CVD) prevention guidelines are generally based on the absolute risk of a CVD event, but there is increasing interest in using heart age to motivate lifestyle change when absolute risk is low. Previous studies have not compared heart age to 5-year absolute risk, or investigated the impact of younger heart age, graphical format, and numeracy. Objective. Compare heart age versus 5-year absolute risk on psychological and behavioral outcomes. Design. 2 (heart age, absolute risk) × 3 (text only, bar graph, line graph) experiment. Setting. Online. Participants. 570 Australians aged 45-64 years, not taking CVD-related medication. Intervention. CVD risk assessment. Measurements. Intention to change lifestyle, recall, risk perception, emotional response, perceived credibility, and lifestyle behaviors after 2 weeks. Results. Most participants had lifestyle risk factors (95%) but low 5-year absolute risk (94%). Heart age did not improve lifestyle intentions and behaviors compared to absolute risk, was more often interpreted as a higher-risk category by low-risk participants (47% vs 23%), and decreased perceived credibility and positive emotional response. Overall, correct recall dropped from 65% to 24% after 2 weeks, with heart age recalled better than absolute risk at 2 weeks (32% vs 16%). These results were found across younger and older heart age results, graphical format, and numeracy. Limitations. Communicating CVD risk in a consultation rather than online may produce different results. Conclusions. There is no evidence that heart age motivates lifestyle change more than 5-year absolute risk in individuals with low CVD risk. Five-year absolute risk may be a better way to explain CVD risk, because it is more credible, does not inflate risk perception, and is consistent with clinical guidelines that base lifestyle and medication recommendations on absolute risk.