Heart-related system In 1995, Drutel et al. [9] reported the expression of OL1 (Olr1654) in the developing rat heart and suggested its involvement in cardiac morphogenesis, where the OR was hardly detectable at the adult stages. As mentioned above, murine PSGRs (Olfr78 and Olr59) are expressed in the hearts of mouse [16] and rat [15], in addition to prostate. In 2007, Zhang et al. [24] reported that ORs (including OR10G4) are expressed in human heart and various organs using reverse transcription–polymerase chain reaction (RTPCR) and microarray. Recently, OR10J5 was found to be expressed in human aorta, coronary artery, and human umbilical vein endothelial cells [25]. In addition, Matrigel plug assay showed that lyral enhances angiogenesis in vivo. These results let us surmise the physiological role of OR10J5 in angiogenesis. Chang et al. [26] showed that a short-chain fatty acid OR, Olfr78, is highly and selectively expressed in oxygensensitive glomus cells of the carotid body (CB). The CB is a chemosensory organ that monitors blood oxygen to control breath [27]. As lactate eventually activates Olfr78 in heterologous expression experiments, Chang et al. [26] proposed that Olfr78 may act as a hypoxia sensor in the breathing circuit, in addition to its role in olfaction. The next year, Zhou et al. [28] applied the single-cell RNA-Seq method to eliminate the contamination of genes derived from other cell types present in the CB to analyze the expression of ORs in CB glomus cells and identified Olfr78 as the most highly abundant OR in the CB in mice. More recently, Jovancevic et al. [29] reported that OR51E1 activation by the application of cognate agonists induces a negative chronotropic effect in human stem cell-derived cardiomyocytes and also provokes negative inotropic activity in cardiac trabeculae and slice preparations of human explated ventricles. These results imply that some ORs that are expressed in heart may be therapeutic targets for the metabolic regulation of cardiac function. A mouse OR—Olfr544, an ortholog of the OR52 family (OR52K1)—was reported to be expressed in the heart of mice [23]. The unexpected cardiac expression of ORs may regulate cell growth and morphogenesis. General studies on OR expression show that ORs are expressed throughout systems and have diverse functions throughout the body of animals (Table 1) [7-11, 13-26, 28-73].