Cardiac outflow in the early developmental stage of a chick embryo is known to be highly variable depending on environmental temperature. To investigate the effects of environmental hypothermia on the blood flow in the outflow tract (OFT) of chick embryonic hearts, microscopic flow images were consecutively captured from chick embryos at HH stage 17 (2.5 days of incubation) at room temperature. Instantaneous velocity field information of blood flow in OFT was obtained using a micro-particle image velocimetry technique. The cyclic variations of the OFT vessel diameter and wall thickness were simultaneously measured. The experimental results show that environmental hypothermia causes bradycardia with a decrease in peak velocity during systole and the occurrence of backflow during diastole in the OFT. These abnormal phenomena seem to be attributed to the suppression of myocardial wall motion under hypothermic conditions.