A case of pyogranulomatous myocarditis and diaphragmatic myositis caused by Bartonella henselae in an 18 months old tricolor female cat in Turkey was reported in this study. The cat had flea infestation before clinical disease onset. The cat showed clinical findings including lethargy, anorexia, dyspnea, hypersalivation, and polydipsia. At necropsy, the myocardium contained numerous 1 to 2 mm, discrete to coalescing, white-grey nodular foci with approximately 250 ml of serosanguineous fluid in the thorax. By Warthin-Starry silver staining, argyrophilic pleomorphic coccobacilli were seen within the myocardial and diaphragmatic pyogranulomatous lesions. B. henselae DNA was detected in heart, kidney and liver tissues by targeting the riboflavin synthase C (ribC) gene by PCR. Using immunofluorescence technique, B. henselae was also visualized in myocardial tissues. This report provides additional evidence in support of an etiological association between pyogranulomatous myocarditis and diaphragmatic myositis and B. henselae infection in cats.