In this study, factors affecting the degree of heat accumulation and amount of carbonyl compound production of e-cigarettes were studied. Structurally, e-cigarettes consist of an electronic circuit device and a cartomizer. The liquid solution of the e-cigarette is vaporized by a coil in the cartomizer, where heat accumulation and carbonyl compound production occur. The relationship between the two were analyzed according to the shape of the coil. X-ray images of the coil shapes within the cartomizer were obtained and classified according to the relative widths of the coils. The degree of heat accumulation and amount of carbonyl compound generation were examined via inhale and exhale tests. The relationships among the relative width of the coil, degree of heat accumulation, and amount of carbonyl compound generation were derived. For optimal design of the cartomizer, it is suggested that the relative width of the coil be set to to 5 or more.