Occurs in adolescence and all higher age groups. This is the most common primary neoplasm of the heart in adults. Remainder can occur anywhere, including the heart valves rarely. Typical lesion is a smooth glistening transluscent firm or soft variegated mass with a broad base attached to or near the fossa ovalis of the left atrium.
Some examples have a papillary structure with a villous surface.
Cut variegated surface jello-like in consistency with fields of gray and dark red shades due to hemorrhages. Cells are thought to be benign mesenchymal primitive anlage, which form other cellular elements of the tumor, including endothelial cells forming atypical vascular channels, fibroblasts, and smooth muscles. Hemorrhages are common. The left atrial myxoma was the model of how a benign tumor can kill by mechanical means in the days before open heart surgery. It mimicked the diastolic murmur of mitral stenosis, and was an unexpected autopsy finding.