We studied 90 patients with congestive myocardial disease documented at cardiac catheterization (46 idiopathic, 39 ischemic, and 5 hypertensive) who underwent M-mode and two-dimensional echocardiograms every 2-3 months for up to 7 years (mean 3.4 +/- 1.6 years, +/- 1 S.D.). All had angiographic evidence of severe left ventricular dysfunction (left ventricular ejection fraction less than 40%), and were on a variety of inotropic, diuretic, and vasodilating drugs. Only 9 were ingesting anticoagulants (5 warfarin and 4 aspirin), those on warfarin had documented pulmonary emboli or deep venous thrombosis. All but 4 patients were in normal sinus rhythm. Only one subject in this group was found to have a myocardial (left ventricular) thrombus. Postmortem examinations of 27 patients confirmed the ultrasound data. Thus, we conclude that cardiac thrombi are unusual in patients with congestive cardiomyopathies and rarely develop over the course of the illness even in the absence of chronic anticoagulation.