Among them, breed of dog, advanced age, and body weight (BW) ≥ 20 kg, as well as degree of mitral valve pathology; left atrial (LA) and left ventricular (LV) dilation and dysfunction; increased LA pressure; right ventricular dysfunction; development of atrial fibrillation (AF) and pulmonary hypertension (PH); and increased concentration of circulating cardiac biomarkers (e.g., NT-pro-BNP) have been associated with a worse prognosis [4–18]. The gene discussed is NPPB; the disease is atrial fibrillation.