NOS3 and coronary vasospasm: Oestrogen has been demonstrated to increase endothelial nitric oxide synthase activity, thereby promoting vasodilation.10 During the late luteal and menstrual phases, circulating oestrogen levels decline to their nadir, potentially reducing vasodilatory capacity and thereby predisposing to coronary vasospasm.11 Taken together, epidemiological observations,7–9 mechanistic insights,2 and case-based evidence1,4,5 support the possibility that oestrogen replacement therapy offers therapeutic benefits in this distinct population.