Journal of Medical Internet Research - International Scientific Journal for Medical Research, Information and Communication on the Internet #Preprint #PeerReviewMe: Warning: This is a unreviewed preprint. Readers are warned that the document has not been peer-reviewed by expert/patient reviewers or an academic editor, may contain misleading claims, and is likely to undergo changes before final publication, if accepted, or may have been rejected/withdrawn. Readers with interest and expertise are encouraged to sign up as peer-reviewer, if the paper is within an open peer-review period. Please cite this preprint only for review purposes or for grant applications and CVs (if you are the author). Background: Web-based and theory-based eHealth interventions for multiple health behaviours appear to be a promising approach for cardiac patients who have been discharged from the hospital, in adopting and maintaining a healthy lifestyle. Until now, no randomized controlled trials have tested this assumption among Chinese rehabilitation patients with coronary heart disease, using an eHealth intervention. Objective: The study aim was to evaluate the effect of an 8-week web-based eHealth intervention in terms of physical activity (PA), fruit and vegetable consumption (FVC), lifestyle changes, social-cognitive outcomes and health outcomes, compared to a waiting control group in Chinese cardiac patients. The intervention content was theory-based on the Health Action Process Approach. Self-reported data was evaluated, including PA, FVC, healthy lifestyle (the synthesis of PA and FVC), internal resources (combination of intention, self-efficacy and planning) and an external resource (social support) of PA and FVC behaviours, as well as perceived health outcomes (Body Mass Index, quality of life, depression). Methods: In a randomized controlled trial, 136 outpatients with coronary heart disease from the cardiac rehabilitation centre of a hospital in China were recruited. After the and exclusion of unsuitable participants, 114 patients were assigned into one of two groups: (1) the intervention group: first 4-weeks on PA and subsequent 4-weeks on FVC; (2) the waiting control group. Two web-based assessments were conducted, including one at the beginning of the intervention (T1, N=114), and one at the end of the 8-week intervention (T2, N=83). The enrolment and follow-up took place from December 2015 to May 2016. Results: The web-based eHealth intervention outperformed the control condition for PA, FVC, internal resources of PA and FVC, and an external resource of FVC, with an Eta² effect size ranging from .06 to .43. Furthermore, the intervention effect was seen in the improvement of the quality of life (F1, 79 =16.36, P< .001, η2=.17). When predicting a healthy lifestyle at follow-up, baseline lifestyle (odds ratio, OR, 145.60, 95% CI 11.24-1886; P<.001) and the intervention (OR 21.32, 95% CI 2.40-189.20; p<.01) were found to be significant predictors. Internal resources for FVC mediated the effect of the intervention on the adoption of a healthy lifestyle (R2 adj=.29; P=.001), indicating that if the intervention increased the internal resource of behaviour, the adoption of a healthy lifestyle was more likely. Conclusions: Patients’ psychological resources including motivation, self-efficacy, planning and social support, as well as lifestyle, can be improved by a web-based eHealth intervention that focuses on both PA and FVC. Such an intervention enriches extended rehabilitation approaches for cardiac patients to be active, and remain healthy in daily life after hospital discharge. Clinical Trial: Clinicaltrials.gov NCT01909349; https://clinicaltrials.gov/ct2/show/NCT01909349 (Archived by WebCite at http://www.webcitation.org/6pHV1A0G1)