To describe the characteristics and etiology of lung nodules after heart transplantation (HT). During a 6-year period 147 patients received HT and 130 survived more than 1 week. Nodular lesions were demonstrated after HT in 13 patients (10%). Median age was 53 years, and all patients were male. Nodules were detected 23 to 158 days after HT (median, 66 days). An etiologic diagnosis was made in all but 1 case: Aspergillus (5), Nocardia-Rhodococcus (4), and cytomegalovirus (CMV) (3). Previous severe infection was present in 50% of the patients and rejection in 33% (75% with nocardiosis). Initially all patients with Nocardia but only 1 patient with aspergillosis were asymptomatic. The most common symptoms were fever (67%) and cough (50%). Central nervous system (CNS) involvement appeared in only one Aspergillus-infected patient. An average of 1.8 diagnostic procedures per patient were performed. Median time to establish a diagnosis was 8 days (0 to 24). Median hospital stay was 36 days and reached 60 in patients with Aspergillus. No patient died, although aspergillosis, which must be suspected in the presence of dyspnea, pleuritic pain, and CNS symptoms, caused the highest morbidity. Overall diagnostic yield was 60% for transtracheal aspiration, 70% for bronchoalveolar lavage, and 75% for transthoracic aspiration. Ten percent of HT patients developed lung nodules that were mainly caused by Aspergillus, Nocardia, and CMV. The time of appearance and some clinical manifestations may suggest the etiology and may help in the empirical treatment.