We diagnosed Barth syndrome with tafazzin (TAZ) variants associated with left ventricular noncompaction cardiomyopathy (LVNC) in a 1-month-old male infant, weighting 3,010 g, born at 40 weeks of gestation. At 14 days of age, the infant presented with cyanosis while crying and was referred to our institution at 1 month of age. Echocardiography revealed that the left ventricular wall was highly trabeculated, with a ratio of noncompacted to compacted myocardium of >2.0 in all segments. At 4 months of age, the patient developed a urinary tract infection and heart failure. Laboratory findings showed neutropenia and an elevated B-type natriuretic peptide level at 207 pg/mL. After admission, he was initially treated with antibiotics, inotropes, and diuretic agents which alleviated the infection and heart failure. Genetic analyses confirmed that the patient and his mother had a TAZ variant, c.461-2A>C, confirming the diagnosis of Barth syndrome. At 2 months of age, the patient showed preserved global circumferential strain but decreased global longitudinal strain on a layer-specific two-dimensional speckle tracking echocardiography. At 9 months of age, both global circumferential and longitudinal strain had decreased, and cardiac rotation showed that both the cardiac base and apex had rotated counterclockwise. The patient died at 12 months of age due to progressive heart failure induced by dilated cardiomyopathy with LVNC. This case suggests the impact of the dilated cardiomyopathy phenotype with LVNC and emphasizes the clinical advantages of estimating cardiac performance using two-dimensional speckle tracking echocardiography in LVNC patients with TAZ variants.