The formation of atrial hematomas with a mass effect in patients who have undergone cardiac surgery originates a clinical and hemodynamic syndrome that is difficult to assess. Hypotension with high right atrial pressure and equalization of pulmonary wedge pressure is not always present due to the irregular distribution of the hematoma in cardiac chambers. Transesophageal echocardiography is a useful diagnostic procedure for atrial hematomas, differentiating them from other similar clinical and hemodynamic situations like left ventricular or prosthetic valve dysfunction. We present five clinical cases of patients who underwent cardiac surgery and presented atrial hematoma, right atrial in four and left atrial in one. All were diagnosed by transesophageal echocardiography. In one case magnetic resonance imaging was used.