Percutaneous transvenous mitral commissurotomy (PTMC) is the first-line therapy of clinically significant rheumatic mitral stenosis. While the procedure is generally safe, new onset or aggravation of mitral regurgitation (MR) may occur, mainly due to commissural splitting and, less frequently, to leaflet tear and chordal rupture. Papillary muscle rupture (PMR) is exceedingly rare in this setting. A 74-year-old woman with a history of aortic valve replacement and prior rheumatic mitral commissurotomy presented for worsening exercise intolerance and exertional dyspnoea. Transthoracic echocardiography showed a mean pressure gradient of 10 mmHg and a mitral valve area of 1.0 cm², consistent with clinically significant mitral stenosis. Subsequent PTMC was complicated by anterolateral PMR. However, the resulting MR was unexpectedly only of mild-to-moderate severity. Because of residual mitral stenosis and persisting symptoms, surgical mechanical mitral valve replacement and tricuspid annuloplasty were performed 6 weeks after PTMC. Papillary muscle rupture was confirmed during surgery. We herein describe the occurrence of PMR induced by PTMC; the resulting MR was unexpectedly of mild-to-moderate severity, as a result of extensive rheumatic lesions limiting valve mobility. This case challenges the dogma according to which PMR invariably leads to severe MR. This might not be necessarily the case when it occurs following PTMC.