Coronary angiogram in the right anterior oblique view showing the filling of the posterior descending artery of an obstructed right coronary artery (RCA) by grade 1 collateral vessel (red arrows) originating from the septal branch of the left anterior descending (LAD) artery. LCA, left coronary artery; Cx, circumflex; SB, septal branch; PDA, posterior descending artery.