After World War II on August 23, 1946 the British military administration in Germany established the new state of North Rhine-Westphalia with the merger of the provinces of Westphalia and North Rhine, the northern part of the Prussian Rhine Province, to which in January 1947 the Free State of Lippe was added. That same year Wolfgang Pagenstecher, a famous German heraldist living in Düsseldorf, made the original blazon for the newly created state, which adopted it on 5 February 1948. On 10 March 1953 this has been confirmed by the Law about the state's colours, the state's coat of arms and the state' s flag.
The named law starts as follows:
§ 1 The state's colors are green-white-red.
§ 2 The state's coat of arms is party per paleVert a bend sinister wavy Argent and Gules a horse rampant Argent, enté en point embowed Argent a rose Gules seeded and leaved Or.
— State Government of North Rhine Westphalia, Law about the state's colours, the state's coat of arms and the state' s flag of March 10, 1953
So the constituent three parts of this coat of arms are:
dexter: Vert a bend sinister wavy Argent, which is a reflection of the former coat of arms of Rhine Province. This until then showed a bend wavy, representing the river Rhine flowing through the Rhineland, today's southwestern part of the state. The change from bend to bend sinister has only been done because of aesthetic reasons.
sinister: Gules a horse rampant Argent, as opposed to the jumping horse in the arms of Lower Saxony, representing Westphalia, the northeastern part of the state. Originally it was the Saxon steed, the emblem of the Saxon stern duchy. It is identical to the preceding coat of arms of the Province of Westphalia.
enté en point embowed: Argent a rose Gules seeded and leaved Or, showing the rose of Lippe. This was the coat of arms of the Principality of Lippe, now the district of Lippe in the east of the state.