Coronary heart disease (CHD) is the most common cause of death in the Western world. In both the USA and the EU it accounts for over 600,000 deaths yearly. Early data showing the benefits n–3 fatty acids provide in preventing CHD disease were obtained using 20:5n–3 and 22:6n–3 fatty acids derived from fish. Recently, however, it has been shown that reduced risks of CHD and other cardiovascular diseases are found with 18:3n–3 fatty acid as well. To determine if 18:3n–3 fatty acids positively influence plasma composition, 32 male Wistar rats were fed ad libitum four isocaloric diets with the energy derived from corn oil (T1), whole chia seed (T2), ground chia seed (T3), or chia oil (T4) for 30 days. At the end of the feeding period the rats were sacrificed, and blood samples were analyzed to determine serum CHOL, HDL, LDL, TG content, hemogram, and fatty acid composition. Chia decreased serum TG content and increased HDL content. Only with the T2 diet was TG significantly (p < 0.05) lower, and only with the T3 diet was HDL significantly (p < 0.05) higher, than the control diet. Chia significantly (p < 0.05) increased the 18:3n–3, 20:5n–3 and 22:6n–3 plasma contents compared to the control diet, with no significant (p < 0.05) difference among chia diets detected. Significant (p < 0.05) improvement in n–6/n–3 fatty acid ratio was observed for all chia diets when compared to the control.