We report that two young adult patients who were initiated with clozapine for severe psychosis during a hospital-wide gastroenteritis outbreak went into severe shock. Neither patient had troponin elevation. Each required left ventricular assist device support for myocarditis. Endomyocardial biopsy revealed lymphocytic myocarditis in one patient and eosinophilic myocarditis in the other. The former patient expired. Polymerase chain reaction testing was negative for Coxsackie virus. These two patients illustrate that myocarditis can occur at usual incipient doses and that there may be an epidemiologic risk associated with gastroenteritis. Although the white blood cell (WBC) count is expected to decrease with clozapine, these patients had persistently elevated WBC counts. In conclusion, physicians should exercise caution when prescribing clozapine, especially for those with diarrhea.