Upregulation of Ca2+ entry through voltage-gated Ca2+ channels by high rates of beating may be involved in the frequency-dependent regulation of contractility (Bowditch "staircase") of the human heart. This process, which is highly sensitive to beta-adrenergic stimulation, may be crucial in adaptation to exercise and stress.

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The constitutive production of interleukin‐6 (IL‐6), a potent hepatocyte‐stimulating factor and B cell‐differentiating factor, was demonstrated in 3 patients with cardiac myxomas. Tumor cells from the only patient who presented with immunologic features produced 14–23‐fold higher levels of IL‐6 than those from the 2 patients who lacked such features. A significant serum IL‐6 level (56 pg/ml), greater than that observed in patients with active rheumatoid arthritis, was also observed only in this patient, with a subsequent return to an undetectable level after surgical removal of the tumor. This was associated with a regression of the immunologic features. This same patient was observed to have an IL‐6‐dependent, proliferative polyclonal plasmacytosis of the bone marrow. These observations demonstrate that an overproduction of IL‐6 by cardiac myxoma cells, in association with a systemic passage of this IL‐6, may be responsible for the immunologic features similar to those observed in true autoimmune diseases such as rheumatoid arthritis.