Particulate materials (PM) less than 10 ${mu}m$ in diameter are of special interest in air pollution because they are respirable and responsible for the increasing mortality rate of lung cancer and cardiovascular diseases. These particles are often referred to as $PM_{10}$ and they are divided into a coarse fraction and a fine fraction which is also often referred to as $PM_{25}$. In this study, we monitored the TSP, $PM_{10},;PM_{2.5}$ concentration of ambient air collected in northern part of Seoul in early spring and measured the concentration of heavy metals; Cr, Mn, Zn, As, Cd, and Pb. All the heavy metals were found in the collected particles and the concentrations were variable in the $PM_{10},;and;PM_{2.5}$ respectively. The detected concentration ranges were Cr: $ND~2,889ng/m^3,;Mn:2.4~257.9ng/m^3,;Zn:ND~353.7ng/m^3,; As:ND~22.3ng/m^3,;Cd:0.1~2.9ng/m^3,;and;Pb:ND~392.2ng/m^3$ in fine particles. Heavy metal toxicity of the particles were also tested in $H_9C_2$ cell line derived from rat cardiomyocytes. As for the results of health risk assessment calculated by unit risk of IRIS, heavy metals in ambient air of Seoul metropolitan area were found to be responsible for the increase of total excess cancer risk. Among them, chromium (hexavalent) was found to be the most risky in fine particles of ambient air collected in the northern part of Seoul in early spring.