Given that my heart-related symptoms do not seem be disappearing with the pneumonia, what is causing them? The cardiologist's initial working hypothesis is that some of the useless proteins produced by the malignant plasma cells (normal plasma cells produce proteins that are assembled into the required types of antibodies) have been deposited in the tissues of the heart, inhibiting the normal functioning of these tissues. This condition is known as "cardiac amyloidosis", and although it would be a somewhat unusual outcome for a multiple myeloma patient (hence my previous lack of awareness of the possibility), it is hardly unheard of.
The cardiologist was reluctant to discuss countervailing measures that could be taken, assuming that his hypothesis proved correct. He asserted that, in that case, it would revert to being a hematological issue, meaning that the ball would be back in the oncologist's court.
An EKG and an echo cardiogram carried out in the cardiologist's office did not -- of course -- uncover any smoking guns. The next step is a cardiac MRI, which is scheduled for early next week.