The aim of this preliminary study is to look how maternal-fetal heart rates and their beat to beat coupling patterns (λ are influenced by injection of β blocker(propranolol) into pregnant mice. Total of 9 fetuses from 9 pregnant female mice type of C57BL/6J were divided into three groups [control (3), β blockade (3) (4 mg), β blockade (3) (10 mg)]. On 17.5-day beat-to-beat maternal and fetal heart rates (MHR and FHR) were simultaneously measured for 20 minutes (10 minutes under normal condition and 10 minutes with saline (to control group) and propranolol (to the β blockade groups) solution by using an invasive maternal and fetal electrocardiogram techniques with needle electrodes. Results show that FHR decrease (p<0.05 for 10 mg) and maternal-fetal heart rate coupling (λ) patterns increases for 10 mg; p<0.05 and no significant changes for 4mg] followed by propranolol infusion (no change with saline). These changes could be caused by propranolol (dosage of 10 mg) which could have transmitted through the placental barrier. The presented results allow for assessment of the dosages of β adrenergic control of maternal and fetal heart, which will further enhance the value of the mouse as a model of heritable human pregnancy and hypertension.