View source for One is Enough, Two is Too Many

{{NHJ|
|mainauthor= '''A.A.M. Wilde, R.B.A. van den Brink'''
|edition= 2005:8,285
}}
[[Image:Puzzle_2005_8_285_fig1.jpg|Figure 1|thumb]]
[[Image:Puzzle_2005_8_285_fig2.jpg|Figure 2|thumb]]
An otherwise healthy 24-year-old man was referred
to our hospital because of drug refractory spells
of palpitations accompanied by dizziness. These
symptoms recurred several times a month and were
terminated with intravenous adenosine. Figures 1 and
2 show the ECGs during palpitations and during
normal conditions, respectively.

'''What is the most likely diagnosis and how can it be treated?'''

[[Puzzle 2005_8_285 - Answer|Answer]]