The aim of this study was to compare the tolerance of seedlings of three Polish buckwheat cultivars (Hruszowska, Kora, and Luba) for short-term exposure to Pb²⁺ and Cd²⁺. Seedlings were grown under controlled conditions in Hoagland nutrient solution, with the addition of low/high Pb²⁺ or Cd²⁺ ions (0.01 and 1.00 mM, respectively). After 3 days of treated seedling growth, the levels of total anthocyanins and content of particular flavonoids were measured. The presence of low concentrations of both Pb²⁺ and Cd²⁺ resulted in a small stimulation of the growth of seedlings of all studied cultivars, while higher doses inhibit root growth and, to a much lesser extent, that of shoots. Cadmium (Cd²⁺) ions were more harmful for growth of buckwheat seedlings than Pb²⁺ ions. More resistant to stress caused by the presence of high concentrations of Pb²⁺ and Cd²⁺ in the growth medium were seedlings of Hruszowska and Luba cultivars, compared to Kora seedlings. Cotyledons of more resistant cultivars (Hruszowska and Luba) contained much more flavonoids than cotyledons of Kora.