Variation of the smallest cardiac veins.
D000818:Animals; D003331:Coronary Vessels / Q000033:anatomy & histology*; D004285:Dogs; D006801:Humans; D012756:Sheep; D013552:Swine; D014680:Veins / Q000033:anatomy & histology*; D014699:Venules / Q000033:anatomy & histology*