The present knowledge of coronary arteries in prenatal diagnosis is reviewed with a focus on three aspects: the physiology and visualization of coronary flow, malformations involving the coronary arteries, and the "heart-sparing effect". Visualization of coronary arteries in a healthy human fetus is possible in real-time and colour Doppler during the last 10 wk of gestation when ultrasound conditions are excellent. Visualization at an earlier gestational age (up to 13 wk) is feasible mainly in association with malformations and impending hypoxia. The main coronary malformations that can be visualized in utero are the ventriculo-coronary communications in fetuses with pulmonary atresia. In the last few years, interest has been focused on the "heart-sparing effect", defined as the increased perfusion of the coronary arteries in fetuses with severe growth restriction and abnormal Doppler velocimetry in the peripheral vessels. Increased perfusion detectable with colour and pulsed Doppler is a late sign of fetal compromise in hypoxaemia. It confirms animal experiments that have demonstrated dilatory reserves of the fetal coronary arteries under chronic hypoxaemia. The outcome of 21 fetuses showing the "heart-sparing effect" before 32 wk gestation was poor: nine fetuses died in utero and two after birth, the median weight at birth was 630 g. In summary, our knowledge of the coronary arteries in the fetus is based on the diagnostic means used in prenatal diagnosis. New information in this field may also contribute to a better understanding of coronary heart disease later in life.