1. A method for increasing the number of temporal cardiac phase images of a patient's heart from NMR data acquired synchrononsly during a succession of cardiac cycles, the steps comprising: a) producing a cardiac signal which indicates phase of the patient's heart during each cardiac cycle; b) acquiring first NMR data at a first cardiac phase during each of said succession of cardiac cycles and storing said first NMR data to form a first data set; c) acquiring second NMR data at a second cardiac phase during each of said succession of cardiac cycles and storing said second NMR data to form a second data set; d) reconstructing a first image from said first data set depicting the patient's heart at said first cardiac phase; e) reconstructing a second image from said second data set depicting the patient's heart at said second cardiac phase; f) selecting NMR data from said first and second data sets to form an intermediate data set; and g) reconstructing an intermediate image from said intermediate data set which depicts the patient's heart at a selected cardiac phase between said first and second cardiac phases.