Abstract: This article reports a case of familial dilated cardiomyopathy (FDCM). A 60-year-old male presented with chest tightness and dyspnea. Echocardiography revealed marked left ventricular dilatation with severely reduced systolic function, accompanied by severe mitral regurgitation and pulmonary hypertension. Coronary angiography showed no significant stenosis, and cardiac magnetic resonance imaging indicated non-ischemic myocardial injury. Genetic testing identified a heterozygous frameshift mutation in the titin (TTN) gene, c.103574_103575del (p.Leu34525ArgfsTer16), in the patient and one of his daughters; this variant has not been previously reported. Combined with the family history, a diagnosis of familial dilated cardiomyopathy was established. This case suggests that TTN gene mutations are important genetic basis of FDCM, and genetic testing in patients with unexplained heart failure may help clarify the etiology and facilitate family screening and genetic counseling.