Background Rupture of the cardiac ventricular wall is a rare and essentially lethal complication of infectious endocarditis valvularis. Case Description We report a case of a 49-year-old female patient with infectious endocarditis of the aortic valve. Following aortic valve replacement, the patient developed a sudden free left ventricular wall rupture. Immediate reoperation was successful. Histopathology revealed a myocardial infarction due to septic thromboembolism causing a phlegmonlike myocardial appearance. Conclusion This is a rare case of a myocardial phlegmon with subsequent cardiac lateral wall rupture in the context of an infectious endocarditis with septic coronary embolism.