The interaction between the cardiac and renal systems is important in determining blood pressure and blood volume, both of which play a role in the vasomotor system and fluid balance. Cardiorenal syndrome (CRS) occurs as a result of a disparity in correlation between the two. In veterinary medicine, cardiovascular-renal axis disorder (CvRD) lacks pathologically and etiologically specific data, but shares common pathophysiological patterns with CRS and CvRD in humans. CvRD is structural or functional damage caused by diseases of the heart or kidneys, or toxins or drugs, resulting in the disruption of normal interactions between these organs and the destruction of one or both organs. The aim of this study is to compare the long-term changes in various indicators, including hypertension, proteinuria and echocardiographic parameters, before and after administration of telmisartan in cats with CvRD. This study found a clear gradual decrease in Urine protein to creatinine (UP/C) ratio and left atrium (LA) diameter in cats with CvRD, after administration of telmisartan. UP/C ratio (p<0.001) was found to decrease significantly over time, after administration of telmisartan. UP/C ratio before telmisartan administration was 0.39 ± 0.255 (Day 0) and 0.29 ± 0.056 on day 30 (Day 30), 0.28 ± 0.040 on day 60 (Day 60), and 0.20 ± 0.128 on day 90 (Day 90) after administration, respectively. LA diameter before telmisartan administration was 17.9 mm ± 1.6 before telmisartan administration (Day 0) and 17.4 mm ± 1.8 on day 30 (Day 30), 16.1 mm ± 1.6 on day 60 (Day 60), and 15.7 mm ± 1.7 on day 90 (Day 90) after administration, respectively. Oral administration of telmisartan to cats with CvRD is effective in improving proteinuria and LA diameter, which is a positive aspect of long-term survival in cats with CvRD.