We report a case of sudden unexpected death of a young woman who was found in a bathtub of hot water. The autopsy concluded that all possible causes of sudden loss of consciousness, except cardiac origin, could be excluded. However, the heart did not show any obvious pathological changes. We used next-generation DNA sequencing (NGS) to examine 73 genes and detected 3 rare, potentially pathogenic variants with minor allele frequencies ⩽1.0%. The pathogenicity of these variants was evaluated using 8 in silico predictive algorithms, and SCN5A_p.Gly289Ser, CACNB2_p.Ser502Leu, and MYH11_p.Lys1573Glu were detected as possible pathogenic variants. Inherited heart disease is a likely cause of sudden unexpected deaths of young people in hot baths, even before the clinical manifestation of the disease. In the future, molecular analysis by NGS may help to predict young to early middle-aged people who could be at risk of sudden arrhythmogenic fatality in hot baths.