  Understanding the nature of field-tuned metamagnetic quantum criticality in
the ruthenate Sr3Ru2O7 has presented a significant challenge within condensed
matter physics. It is known from experiments that the entropy within the
ordered phase forms a peak, and is unexpectedly higher than that outside, while
the magnetoresistivity experiences steep jumps near the ordered phase. We find
a challenging connection between Sr3Ru2O7 and heavy-fermion metals expressing
universal physics that transcends microscopic details. Our construction of the
T-B phase diagram of Sr3Ru2O7 permits us to explain main features of the
experimental one, and unambiguously implies an interpretation of its
extraordinary low-temperature thermodynamic in terms of fermion condensation
quantum phase transition leading to the formation of a flat band at the
restricted range of magnetic fields B. We show that it is the flat band that
generates both the entropy peak and the resistivity jumps at the QCPs.
