Introduction: Nonadherence may cause severe health problems in heart transplant (HTx) recipients. Research Questions: The present study aimed to investigate adherence to prescribed medication and recommended lifestyle habits in post-HTx patients and to assess associations between adherence, quality of life (QOL), and psychological well-being. Design: A questionnaire package was sent to all HTx patients from our clinic (n ¼ 858) to answer questions anonymously on medication adherence, dietary recommendations (avoidance of raw animal products and ice cream), pet keeping (risk of zoonosis), anxiety and depression, QOL, and posttraumatic stress disorders. Results: Of the contacted patients, 524 (61%) responded and 505 fulfilled the inclusion criteria (age !18 years and ability to understand German). Of the study participants, 72.4% reported taking their medications very correctly, 72.2% stated consuming alcohol less often than once a week, 58.3% performed physical exercise at least once a week, one-third reported eating nonrecommended foods, 22.1% stated pet keeping, and 4.3% reported smoking. Adherence to prescribed medication was positively associated with age (P < .001) and mental QOL (P ¼ .015) but was unrelated to eating nonrecommended foods (P > .05). Depressiveness correlated inversely with physical QOL (r ¼ À0.232; P < .01) and mental QOL (r ¼ À0.411; P < .01). Stress disorders and minor stressful events were reported by 7.8% and 46.6%, respectively. Stress disorders correlated inversely with mental QOL (r ¼ À0.282; P < .01) and physical QOL (r ¼ À0.422; P < .01). Discussion: Many HTx patients adhere to prescribed medications and health advice. Nevertheless, nonadherence is a problem, especially in younger HTx patients, indicating the need for a nonadherence crisis intervention program for long-term HTx patients.