The conventional X ray film examinations and the angiocardiographic features of 13 cases of constrictive pericarditis are analyzed and compared with those in 5 cases of pericardial effusion and 4 cases of congestive cardiomyopathy. The conventional X ray film examination can contribute to the diagnosis of constrictive pericarditis if the following combination of features is present: absent to moderate cardiomegaly with poorly pulsating straightened heart borders, together with left atrial enlargement and signs of pulmonary venous hypertension. The angiocardiographic features described in the literature for the diagnosis of constrictive pericarditis are confirmed, namely, reflux of contrast material into the dilated inferior vena cava, straightening of the opacified right atrial lateral border, increased thickness of the right atrial extraluminal shadow, straightening of the opacified right ventricular cavity's septal border, and increased pulmonary circulation time. It is stressed that the following signs, not widely appreciated, should prove helpful for the diagnosis of constrictive pericarditis: not only straightening but concavity of the right atrial lateral border persisting throughout the cardiac cycle, not only straightening but concavity of the septal border of a small right ventricular cavity, a small left ventricular cavity displaying forceful contractions, and a concavity of the parietal border of the left ventricular cavity. It was noted in the patients that left atrial enlargement and pulmonary venous hypertension were the rule rather than the exception. These features may be particularly helpful in the differentation of constrictive pericarditis from pericardial effusion in which the cardiac cavities are of normal size, shape and display normal contractility, or from constrictive cardiomyopathy in which there is dilatation of these cavities with diminished contractions.