This is a report of a child who died at 20 months from what was clinically 
thought to be cardiomyopathy of unknown etiology. Barth syndrome, an X-linked 
mitochondrial cardioskeletal myopathy, was diagnosed by genetic testing at 
autopsy. Barth syndrome presents in infancy or childhood with cardiomyopathy, 
hypotonia, growth delays, and cyclic neutropenia. Other associated laboratory 
findings can include hypocholesterolemia, relative monocytosis, low prealbumin, 
low plasma carnitine, and lactic acidosis. The classic echocardiogram finding is 
left ventricular noncompaction, although not always present. Until recently, the 
most reliable biochemical finding has been 3-methylglutaconic aciduria. However, 
quantitative analysis must be specifically requested for results to be reliable. 
Recently, a confirmatory tetralinoleoyl cardiolipin high-pressure liquid 
chromotography-tandem mass spectrometry blood test has become available. Genetic 
testing is also confirmatory and details the underlying mutation. Diagnosis is 
often missed or delayed and early diagnosis improves survival. The purpose of 
this case report is to encourage physicians to include Barth syndrome in the 
differential for cardiomyopathy of uncertain etiology in males, especially in 
the presence of growth delays, hypotonia, neutropenia, and/or family history of 
pediatric male death of unknown etiology.