Managing right-sided chronic heart failure (CHF) due to tricuspid regurgitation (TR) remains a clinical challenge. Tolvaptan (TLV), a vasopressin V2 receptor inhibitor, is effective in controlling decompensated HF. However, its effects on right-sided CHF caused by TR are unclear. We sought to clarify the effects of TLV in CHF patients complicated with TR. The cohort consisted of 33 CHF patients with moderate or severe TR and permanent atrial fibrillation, who required hospitalization for HF. We observed 19 patients treated with TLV plus conventional therapies (TLV group) and 14 patients with conventional therapies alone (conventional group). Clinical characteristics, echocardiographic parameters, and laboratory data were investigated. Baseline characteristics were similar between groups. In the TLV group, the severity of TR at admission was 73.7% moderate and 26.3% severe. In the conventional group, these percentages were 85.7% and 14.3%, respectively. During the follow-up, the severity of TR improved in the TLV group (trivial–mild: 52.6%; moderate: 36.8%; severe: 10.5%) ( p  < 0.01). However, it did not improve in the conventional group (trivial–mild: 21.4%; moderate: 50.0%; severe: 28.6%) ( p  = 0.08). The diameter of the tricuspid annulus ( p  < 0.01), basal ( p  = 0.02), and mid right ventricle ( p  = 0.04) was reduced at follow-up in the TLV group. Nevertheless, these parameters did not change in the conventional group. Serum creatinine levels were maintained ( p  = 0.74) in the TLV group, but deteriorated in the conventional group ( p  = 0.03). TLV reduced right ventricular dimensions and improved TR without deterioration of renal function. Thus, TLV may be a new drug for the treatment of CHF patients with TR.