The aim of this study was to develop and examine the effectiveness of a 4-week Mobile Health (mHealth) programme using the smartphone app Care4Heart on awareness, knowledge, perceived stress, and a heart-related lifestyle among working population in Singapore. A quasi-experimental single group pretest and repeated post-test design. A total of 160 nonhealth-related working adults were recruited from February 2016-April 2016. The Care4Heart app was installed on the participants' phones. Outcome measures, including the Heart Disease Fact Questionnaire-2, the Behavioral Risk Factor Surveillance System, and the Perceived Stress Scale were collected online at baseline, 4th week, and 6th month from baseline. Compared with the baseline, the participants had significantly higher total mean scores for awareness and knowledge of coronary heart disease (CHD) after study intervention at 4weeks and 6months from baseline. However, there were no significant differences in perceived stress levels and heart-related lifestyle behaviours before and after the intervention. The study contributed some evidence that the mHealth app helped to improve awareness and knowledge of CHD. Coronary heart disease remains one of the major causes of death and disability. It imposes a heavy financial burden on working adults. However, working adults were less able to identify the risk factors and adopt healthy lifestyles due to gaps in knowledge and awareness. This study demonstrated some effects of a mHealth programme in improving awareness and knowledge of CHD among the working population. mHealth provides a potential avenue for primary prevention of CHD.