As the heart is made up of fibroblasts, myoblasts, and endothelial cells in addition to cardiomyocytes [44], it is likely that increased 5-HT expression in heart failure also induces the upregulation of the 5-HT2A receptors in these cells, thereby increasing 5-HT2A receptor expression in TAC mice. The gene discussed is HTR5A; the disease is heart failure.