Concentrations of the heavy metals (Fe, Zn, Pb, Cu, Cd and Co) were assessed in water, sediment and the soft tissues of three length classes of the edible bivalve Venerupis decussata. The specimens were collected monthly from the Egyptian Mediterranean Sea coast of Port Said city during the period from December 2015 to November 2016. The mean concentrations of heavy metals in water were 4.44, 0.06, 0.04, 0.44, 0.54 and 0.45 for Fe, Zn, Pb, Cu, Cd and Co μg/L, respectively. The corresponding concentration values in the sediment were 21.7, 6.33, 0.55, 10.65, 2.30 and 1.39 μg/g dry weight for Fe, Zn, Pb, Cu, Cd and Co, respectively. However, these metals were assessed in the soft tissues of three length classes of V. decussata. A negative relationship between the bivalve size and metal concentration was identified, which states that the smallest individuals contained the highest concentrations of metals. Food quality and uptake of heavy metals in tissues of V. decussata generally varied along size gradients, with peak values in small-sized individuals. The possible public health threats from dietary exposure to the heavy metals were evaluated.