Background Patient-reported outcomes (PROs) which demand special attention and immediate help are referred to as PROs alert. Suicidal ideation (SI) is one of the PROs alerts which are insufficiently investigated. The aim was to assess the prevalence and risk factors for SI in patients following cardiac surgery. Methods A total of 190 patients (mean age: 66.09, SD = 10.19; 57 women) were assessed at three months following cardiac surgery. SI was identified using the Patient Health Qustionnaire-9 (PHQ-9) question. The Hospital Anxiety and Depression Scale-Modified was used to assess anxiety, depression, and irritability. Additionally, self-perceived health improvement and level of hope were assessed using the Likert scale. Dyspnea and chest pain were assessed using a visual analogue scale. Results SI was observed in 14.7% of participants. Patients experiencing SI had significantly higher levels of depression, anxiety, irritability, dyspnea and chest pain. They perceived the surgery to be less effective and had lower levels of hope. No significant relationships were found regarding age, sex, employment status, myocardial infarction, heart failure, operation mode, type of procedure, extracorporal circulation, hospital stay and postsurgical complications. Logistic regression revealed female sex (B = 2.363), higher anxiety level (B = 0.451) and older age (B = 0.062) to be risk factors for SI. The total variance explained by the model was 46%. Conclusions Assessing suicidality and negative emotions with special emphasis on anxiety simultaneously with somatic complaints is vital to address PROs alerts and improve care for patients following cardiac surgery. In-depth evaluation and psychological care are recommended in case of positive screening.