In addition to the need to identify Pip-PMOs with high efficiency and cardiac delivery, it was a further aim to better define those elements of the hydrophobic core of Pip peptides that are important for heart delivery. To this end, Pip peptides containing partial deletions of the hydrophobic core by 1 aa (removal of tyrosine; Pip6c) and by 2 aa (removal of isoleucine and tyrosine; Pip6d) were synthesised as PMO conjugates (Figure 1a) .