We studied the feasibility of transesophageal echocardiography to guide endomyocardial biopsies in five heart transplant patients and two baboons with heart transplantations. The patients were 1 month to 1.5 years old with weight range of 2.9 to 9.5 kg. The two juvenile baboons weighed 6.6 and 7 kg. Transesophageal echocardiography was performed uneventfully in all cases with the use of sedation and anesthesia, which were necessary for catheterization. The combination of four-chamber and short-axis views easily identified the exact location of the bioptome within the heart, views that fluoroscopic imaging could not provide. Transesophageal echocardiography proved to be a safe and useful tool for guiding the endomyocardial biopsy procedure. With further refinement endomyocardial biopsy with only transesophageal echocardiography guidance could become the routine method for endomyocardial biopsies in infants, particularly when there are abnormalities of heart situs or position.