In explanation of the fact that fibrinous clots are almost universally found on the _right_ or _venous_ side of the heart, notwithstanding that arterial blood is richer in fibrin than venous, the following has been suggested to my mind: _First._ While venous blood contains a smaller proportion of fibrin, may not its deoxydized condition favor the more ready deposit of this substance, than by the more highly vitalized arterial blood? _Second._ The feebler muscular power of the right side of the heart would necessarily be attended with a slower circulation through its cavities, the partial stasis of the blood giving another condition favorable for the formation of a clot; and _Third._ The valves of the right side of the heart, present three flaps or folds, instead of two as on the left, and hence, with their numerous tendinous cords, offer an increased number of obstructing points, around which the deposit may be made. These several circumstances would seem sufficient to account for the admitted fact. _Symptoms._ The symptoms attending the formation of fibrinous clots in the heart, are usually sudden in their accession, frequently attended with a chill, and marked by great oppression in breathing, coldness of surface, and _pallor of face and lips_, the latter symptom distinguishing from the dyspnœa attending croup, asthma, pneumonia, etc., where the face is _livid_ from venous congestion. The pulse is usually rapid and feeble; the action of the heart labored, palpitating, and sometimes intermitting, while auscultation will reveal a tumultuous churning-like action, the normal sounds being quite undistinguishable. Pulsation of the jugulars will be present in most cases, and where the clot greatly obstructs the play of the tricuspid valves, a double pulsation will be likely to be noticed. In the last stage, a copious cold perspiration appears upon the whole surface of the body.