Contemporary understanding of acute pericarditis rests on 3 main considerations: (1) pericarditis occurs in every category of disease, common and exotic (the spectrum is so broad that with every new case, the clinician should devise an appropriate differential diagnosis) (2) to avoid therapeutic mishaps, pericarditis must not be mistaken for other syndromes, and (3) the etiological and clinical spectra of acute pericarditis change frequently and some classic assumptions and descriptions, perpetuated in some publications, are outdated. Except immunocompromised individuals, especially in patients with acquired immunodeficiency syndrome, there has been a sharp decline in infectious pericarditis. Tuberculous pericarditis has declined markedly in developed countries.