Circumferential pericardial effusion typically results in biventricular tamponade and equalization of intracardiac and pericardial pressure during diastole. However, tamponade may involve the right or left ventricle. While isolated left ventricular cardiac tamponade (LVCT) can occur as a postoperative complication from localized posterior pericardial effusions, circumferential pericardial effusions leading to LVCT are rare. We report a case of a patient with severe pulmonary hypertension, a large nonloculated pericardial effusion, and LVCT, which was probably due to a chronic undifferentiated connective tissue disorder. This case illustrates that when evaluating patients with circumferential pericardial effusions and associated pulmonary hypertension, the typical findings of cardiac tamponade (pulsus paradoxus, right ventricular diastolic compression and hypotension) may be masked. The echocardiogram must be reviewed carefully as it may reveal left ventricular diastolic compression, the hallmark of LVCT, which may significantly compromise left ventricular filling and cardiac output.