RGS4 and atrial fibrillation: Absence of regulator of G-protein signaling 4 (RGS4) predisposes to atrial fibrillation and is associated with abnormal calcium handling [33] and activation of RGS4 mediates the cardioprotective effects of natriuretic peptides in the heart [34], of which natriuretic peptide A, NPPA, was also significantly down-regulated by trastuzumab and lapatinib.