The heart is an amazing organ. It beats once per second, about 2 billion times by the time we retire, and if it stops – so does life. The volume it pumps in a year is equivalent to that of an Olympic-sized swimming pool. Pumping itself involves intra-cardiac volume redistribution between atria and ventricles, without a discernible change in the overall external volume occupied by the blood-filled heart. This mechanical activity results from electrically-orchestrated contractions of billions of individual heart muscle cells. Each of them displays slightly different stress-strain behaviour, depending on the local mechanical environment which differs as a function of basico-apical and transmural position. The mechanical environment furthermore changes differentially with any alteration in pre- (volume) or after- (pressure) load, such as on every breath we take, when we change posture, or during exercise. The matching of local mechanical activity to global demand requires finely tuned auto-regulatory abilities, and all that in the absence of the kind of neuro-muscular junctions that tune skeletal myofibre activity. In addition, the cross-talk between electrics and mechanics is far from uni-directional, as electrical excitation and conduction, as well as the mechanisms underlying electro-mechanical coupling, are exquisitely mechano-sensitive. Add to this the observation that the heart contains more non-myocytes than muscle cells, combined with recent insight into electrical coupling between those different cell populations, and it becomes clear that we need to take a fresh look at the intriguing aspects of cardiac structure and function that extend beyond current textbook knowledge. This lecture will address some of those aspects that may be of relevance on the path towards an integrated understanding of the heart.

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