Phenyl piperazine anti-arrhythmia agents

A compound of the formula:

• ##STR11## or a pharmaceutically acceptable salt thereof, wherein
• R is R.sup.3 SO.sub.2 NH--, R.sup.3 CONH--. R.sup.1 R.sup.2 NSO.sub.2 --, or
• R.sup.1 R.sup.2 NCO--;
• R.sup.1 and R.sup.2 are each independently H or C.sub.1 -C.sub.4 alkyl;
• R.sup.3 is C.sub.1 -C.sub.4 alkyl, C.sub.3 -C.sub.7 cycloalkyl or NR.sup.1 R.sup.2 ;
• and
• "Het" is 2, 3 or 4-pyridyl optionally substituted by one or more substituents each independently selected from C.sub.1 -C.sub.4 alkyl and NH.sub.2 ;
• or 2-imidazolyl optionally substituted by one or more C.sub.1 -C.sub.4 alkyl groups.