Why do some people with lung disease often die of heart failure?

The heart is the first organ to be affected by lack of or shortage of oxygen. This is a sad but true fact. I know it first hand. Because of the shortage of oxygen the heart works harder and expands only making the muscle it is, weaker.
I have emphysema/COPD and know full well what it is doing to me.

The heart and lung are in series and as such, any pathology of the lung which makes it hard for the heart to push blood to the lungs via the pulmunary aa. will cause undue strain on the heart.

the right side of the heart pump blood through arteries that like a branch of a tree get smaller and smaller (arterioles and capillaries that ends in the lungs... the blood has to go through these capillaries (in the lungs) and go back to the left side of the heart, where it goes back to the body.... if there are certain disease like emphysema or restrictive lung disease , the pressure gets so high (pulmonary pressure) that cause the heart that acts as a pump over time (months or years) to fail, and the person develops what is called heart failure (a poor pump that gives up... same thing happens with hypertension)

because the cardiovascular system and the respiratory system work together to get oxygen to all the organs throughout the body, including the heart muscle it's self. the blood goes throught the right atrium and ventricle then through the pulmonary artery that branched into other arteries that go into the lung, there the blood collects oxygen and is taken through pulmonary veins where it is taken back into the heart into the left atrium and ventricle where is goes through the aorta and then on to every organ into the body put simply. the heart being an organ/muscle it also needs oxygen to function, so if someone suffers lung disease thats how they can die of heart failure.