A B S T R A C TMyopericarditis is a rare but well-documented clinical presentation of primary Toxoplasma gondii infection in immunocompetent patients. Here, early detection of Toxoplasma DNA in the peripheral blood by PCR allowed the diagnosis of acute toxoplasmosis while serological tests were negative. Additional serological evaluations 2 weeks later confirmed the diagnosis and showed that cardiac manifestations occurred before seroconversion. This highlights the importance of a second serological control in the case of a suspected active infection. Overall, we show here that PCR testing for Toxoplasma is a sensitive and straightforward alternative to serological examinations.