Severe tricuspid regurgitation is especially caused by pulmonary hypertension. Primary tricuspid regurgitation in the absence of pulmonary hypertension and of unknown etiology is a very rare condition with scarce data about its diagnosis, treatment, and follow-up. The particularities of surgery indication and outcomes are still not clearly known. A 72-year-old woman with a medical history of coronary artery bypass grafting three years ago presented with shortness of breath and low limb edema. Physical examination revealed a prominent bilateral jugular turgescence, hepatomegaly, peripheral edema, and a left midsternal border holosystolic murmur, suggestive of tricuspid regurgitation. The echocardiogram confirmed the diagnosis and showed preserved right and left ventricular dimensions and function. Coronary angiography showed no new obstructive lesions and patent surgical grafts. Right cardiac catheterization revealed mild pulmonary hypertension and increased right atrium pressure. Cardiac magnetic resonance showed mild right ventricular dilation with normal systolic function and normal left chambers. No late gadolinium enhancement was detected. Because of persistent symptoms, even after optimization of medical therapy, the patient was submitted to tricuspid valve replacement surgery. Immediately after the surgery, the patient developed significant right ventricular dysfunction, with the need of continuous hemodynamic support. She had progressive clinical recovery that was confirmed by serial echocardiograms that showed improvement in right ventricular volume and function. The patient was discharged with no signs or symptoms of right heart failure. The histopathological examination showed significant and diffuse myxomatous degeneration of the leaflets. No signs of infection or vegetation nor disruption of strands were observed. This report illustrates a very rare case of symptomatic primary isolated severe tricuspid regurgitation caused by myxomatous degeneration of the leaflets. The thoroughly diagnostic workup is presented, and only the histopathological analysis of the leaflets revealed the etiologic process. Surgical treatment indicated before the onset of right ventricular failure was essential to patient's full recovery.