A 45 year old man, 10 weeks after angioplasty and endoprosthesis insertion for myocardial infarction, developed tamponade in an infectious context. RNA 16S investigation, using the universal amplification method with ribotyping, detected Porphyromonas gingivalis (a strict anaerobic bacillus associated with peridontitis) in the pericardial fluid. This appears to be the first description of such a clinical scenario, and suggests 5 aetio-pathological mechanisms: fissure syndrome, malignant tamponade, post-infarction pericardial syndrome, endoprosthesis infection and infectious tamponade. We also describe the ribotyping method, which by amplifying DNA coding for RNA 16S allows identification of an increasing number of micro-organisms implicated in infectious pathology.