This study was conducted in a cross-sectional correlation design to identify factors affecting the practice of COVID-19 prevention activities in patients with heart diseases. A convenience sample of 195 patients with heart diseases from one tertiary teaching hospital completed questionnaires with items from the characteristics of these participants, their knowledge, attitude, and practice related to COVID-19 prevention activities. Participants’ knowledge, attitude, and practice for COVID-19 prevention were relatively high but there was a significant difference in the degree of practice of COVID-19 prevention activities according to the characteristics of the participants. The higher the level of their knowledge and the more positive their attitude, the higher their practice. Attitude and information check about COVID-19 prevention were factors that influenced the practice of COVID-19 prevention activities, with an explanatory power of 32%. This study can help motivate and actively encourage COVID-19 prevention practices.