The magnetic interactions in the ferromagnetic Heusler alloys X2MnY (Pd2MnSn, Ni2MnSn and Cu2MnAl) have been investigated using neutron scattering. The spin wave dispersion relations along the [100], [011] and [111] directions have been determined across the whole magnetic Brillouin zone. The results have been analyzed in terms of spin wave theory with the assumption that only Mn atoms have a localized magnetic moment. It has been found that interactions between more than sixth neighbors (R≳11 Å) should be taken into account to reproduce the observations with a theoretical relation h/ω?=2S(J(O)−J(q↘) ). The exchange integrals JR at large distances have an oscillatory character which can be interpreted by the s‐d type interaction based on the nearly free electron model. However the n.n and n.n.n interactions have opposite signs to those expected from the model. These interactions depend strongly on the kind of X atom and Cu atoms have the largest effect. The spin wave renormalization found in Pd2MnSn could also be interpreted by the spin wave theory with dynamical interactions. Neutron paramagnetic scattering for Pd2MnSn gives an energy spectrum of Gaussian shape with the second momentum in good agreement with the value calculated using the exchange parameters determined from the spin wave study. All these facts suggest that the Heusler alloys can be classified as typical Heisenberg systems with long range interactions.