Here we provide background information for the pathobiological concept of a "sick lung circulation", and how it may affect cardiac function. We propose that in most chronic and progressive lung diseases, but in particular COPD/emphysema and interstitial lung diseases (ILD), there are significant pathological changes of the small pulmonary vessels. Complementing the WHO classification of pulmonary vascular diseases we provide a classification which is based on pathogenetic mechanisms such as inflammation, hypoxia and angioproliferation. We also propose that chronic lung disease - related 'cor pulmonale' is insufficiently explained by an elevation of the pulmonary arterial pressure. © 2012 Bentham Science Publishers.