Up to 40% of cases of erectile dysfunction (ED) originate from vascular disturbances associated with atherosclerotic disease, leading to the previously proven concomitance between ischaemic heart disease (IHD) and ED. The aim of this study was to evaluate patients' knowledge about modifiable risk factors for ED. The evaluated group of patients was composed of 502 male patients undergoing cardiac rehabilitation and receiving treatment for IHD. The patients' knowledge of risk factors for ED linked to IHD was assessed with an original survey. The presence of ED was assessed using an abridged version of the International Index of Erectile Function-5 questionnaire. Increase in leisure-time physical activity was estimated using a leaflet based on the Framingham questionnaire. In all, 189 participants were unable to name any modifiable ED risk factors, and only 31 patients knew all 6 of them. The most frequently mentioned ED risk factor was smoking, whereas the least frequently mentioned was sedentary lifestyle. Awareness of smoking as an ED risk factor was closely related to the patients' level of education, place of residence, smoking and underlying ED in the individual patient. The ability to classify diabetes as a risk factor for ED was significantly related to the patients' level of education, place of residence, and the prevalence of diabetes in the evaluated group of respondents. The same relations were observed regarding hyperlipidaemia. Awareness of the negative impact a sedentary lifestyle has on the erectile process was found to be closely related to the patients' age, as well as their level of education. The performed study demonstrates the poor knowledge of IHD patients about the modifiable risk factors for ED. The factor that patients are the least aware of is sedentary lifestyle, which, simultaneously, is the risk factor that most frequently affects the respondents.