inducible ischaemia

hello sir ,
              my father age is 55 yrs and he does not smoke ciggarette at all his sugar is as follow FASTING 89 and PP 143  his BP is 130\90 he take AMLPPERS AT 50 mg one time and GLIZID M twicw a day on jan 2011 he got chest pain we got to dr tell that it is the sign of angina tha pian long only for 10 to 15 sec and then goes on his all ECG report is normal and is TORPTY  test was also negative but when went for TMT test the test was positive for INDUCIBLE ISCHAEMIA the dr give the following medicine NITOCONTIN 2.6 MG twicw a day  and ECOSPRIN AV and RAMIPRIL 5 mg once a day after taking this medicine he never got any chest pain till today and he also walk an hour a day but few days before we go to dr for check up the dr replace  IMDUR 30 mg in place of NITROCONTIN 2.6 mg and said that NITROCONTIN 2.6 mg has side effect when it take for long time ............i want to know that it is ok to take IMDUR in place of NITROCONTIN or not .