I present new results from the PdBI Arcsecond Whirlpool Survey (PAWS, PI: E. Schinnerer), which has mapped the CO emission in M51 at ~40 pc resolution and is sensitive to giant molecular clouds (GMCs) with masses above 105 Msun. Unlike the CO emission in two nearby dwarf galaxies (M33 & the LMC), which mostly arises in discrete clouds, much of the CO emission in M51 resides in bright kpc-sized structures that bear little resemblance to local clouds. Within the inner disk of M51, we find significant variations in i) the properties of the CO emission, ii) the shape of the GMC mass spectrum, and iii) the ratio of the star formation rate and molecular gas surface densities. These variations are mostly related to the dynamical environment in which the molecular gas is located.