Objectives To study older peoples’ experiences with an interactive internet platform for cardiovascular self-management, to assess which factors influence initial and sustained engagement. To assess their views on future use within primary care. Design Qualitative semistructured interview study, with thematic analysis. Setting Primary care in the Netherlands. Participants People ≥65 years with an increased risk of cardiovascular disease who used the ‘Healthy Ageing Through Internet Counselling in the Elderly’ internet platform with remote support of a coach. Participants were selected using a purposive sampling method based on gender, age, level of education, cardiovascular history, diabetes, duration of participation and login frequency. Results We performed 17 interviews with 20 participants, including three couples. In the initial phase, platform engagement was influenced by perceived computer literacy of the participants, user-friendliness, acceptability and appropriateness of the intervention and the initial interaction with the coach. Sustained platform use was mainly facilitated by a relationship of trust with the coach. Other facilitating factors were regular automatic and personal reminders, clear expectations of the platform, incorporation into daily routine, social support and a loyal and persistent attitude. Perceived lack of change in content of the platform could work both stimulating and discouraging. Participants supported the idea of embedding the platform into the primary care setting. Conclusions Human support is crucial to initial and sustained engagement of older people in using an interactive internet platform for cardiovascular self-management. Regular reminders further facilitate sustained use, and increased tailoring to personal preference is recommended. Embedding the platform in primary healthcare may enhance future adoption. Trial registration number ISRCTN48151589; Pre-results.