Mice homozygous for the lack of inward-rectifying potassium channel Kir6.1 gene are disclosed. The mice causes a high incidence of sudden death associated with arrhythmia (atrioventricular block) caused by spontaneous cardiac ischemia, a condition similar to Prinzmetal angina (variant angina) in human, representing an animal model of Prinzmetal angina. Mice heterozygous for the lack of inward-rectifying potassium channel Kir6.1 gene are also disclosed, which are used as parent mice for reproduction of the homozygous mice.