In 1949, Epstein (1) reported 3 cases of left atrial calcification in rheumatic heart disease diagnosed roentgenologically during life and noted that only 2 other such cases appeared in the literature. Since that time numerous other reports have been published (2–6). Although somewhat less than half of the recorded cases have been accompanied by necropsy data (2, 3), stress has been laid upon the probable endocardial location of the calcium. Attention has been invited to the rheumatic endocardial lesion of MacCallum (7) as the probable calcium nidus (1). The frequency of the MacCallum lesion in rheumatic heart disease has also been noted, as well as the probable infrequency of calcific deposits within it (1, 8). As a basis for this report, x-ray film studies and the recorded fluoroscopic findings of 300 patients examined prior to mitral commissurotomy for the relief of mitral stenosis were reviewed. Eight cases of left atrial calcification were found. In all but 2 instances the tip of the atrial appendage was amputated at operation and submitted for pathologic study with special reference to the occurrence of calcification as demonstrated by the von Kossa stain method. Calcification (roentgenologically “visible” and surgically palpable) was encountered in the area of the auricular appendage in 5 of the 8 cases, and in 3 of these the detectable calcification was limited to that area. In the 3 remaining cases linear marginal calcification was demonstrated in the body of the left atrium, but did not involve the appendage. Mitral annulus and valvular calcification are not included in this study. The x-ray finding of a curved linear calcium density within the margin of the left artium in rheumatic heart disease seems consistent with intramural calcification. If the calcium deposition is laminated or relatively thick, the presence of calcified thrombus should be strongly considered. Obviously, calcified thrombus and intramural calcium could coexist, but roentgen recognition of this combination would seem rather uncertain. The accompanying illustrations and the data in the legends are from the records of 8 cases of rheumatic heart disease surgically explored for the relief of mitral stenosis (finger exploration of the interior of the left atrium and mitral commissurotomy) (Figs. 1–8). To the best of our knowledge all of the 8 patients are still living. Discussion Our small series substantiates the probable intramural location of calcium within the body of the left atrium when it is radiologically seen in a linear, non-laminated, marginal distribution. Relative thickness or lamination of the calcium deposition, as mentioned above, should suggest calcified thrombus. While the same reasoning may well apply to the appendageal portion of the left atrium, thrombosis has a high incidence at this site and calcification in this area, regardless of distribution, may represent thrombus calcification. The possibility of this is suggested by Case 3.