A 52-year-old man underwent mitral valve repair for mitral regurgitation. Four months postoperatively, the patient developed dyspnoea, fatigue and dark urine. He presented to his primary care physician 6 months postoperatively, where an evaluation revealed anaemia and mild renal failure. The haemoglobinuria was misdiagnosed as gross haematuria and the patient consequently underwent several unnecessary invasive urological exams. A transthoracic echocardiogram showed a recurrent mitral regurgitation that was considered non-significant, before performing additional laboratory testing and a renewed echocardiogram. The above results showed evidence of haemolysis and a mild to moderate mitral regurgitation, although with a high velocity jet. The patient was diagnosed with haemolytic anaemia that necessitated blood transfusions and a reoperation with a mechanical valve, after which the patient made a full recovery. Importantly, it was mainly the velocity of the jet and not the severity of the mitral regurgitation that caused the mechanical trauma to red blood cells.