Eighty patients with pericardial constriction confirmed by catheter data were studied by CT (n = 79), MR imaging (n = 24), or both. To determine the validity of these imaging methods for subsequent treatment, 30 patients' studies were evaluated retrospectively (1980-1984) and 50 (1985-1991) prospectively. Twenty patients from the first group and 30 patients from the second group underwent pericardiectomy. By systematic analysis of CT scans and MR images it was possible to characterize the morphology of pericardial constriction (n = 80); to identify global (n = 27), right-sided (n = 46), left-sided (n = 2), annular (n = 2), effusive (n = 2), and epicardial (n = 1) forms of pericardial constriction; and to define parameters of myocardial atrophy and fibrosis (n = 17). Seventeen patients had myocardial atrophy, fibrosis, or both. Seven of them underwent pericardiectomy; all died of acute myocardial failure (100%). Four (9.3%) of 43 patients without myocardial atrophy or fibrosis died as a consequence of other complications. The method of thoracotomy and periepicardiectomy was continuously adjusted to the preoperative CT and MR findings. Thus, the clinical use of CT and MR imaging in patients with known or suspected pericardial constriction is based on (a) exclusion of patients with restrictive hemodynamics from diagnostic thoracotomy, (b) preoperative determination of the method of thoracotomy and extent of pericardiectomy, and (c) exclusion of patients with myocardial atrophy or fibrosis from pericardiectomy.